Only the George Lucas and the costume designers would be able to tell you for sure what the uniform colors mean, but it’s never been fully explained by any of them.
Being a more technically-minded “Star Wars Freak” than Redeemer, I’ve pieced together from the movies, novels, card games, RPG’s, and real-world history what the cap and uniform colors might actually mean.
When it comes to explaining the difference between the Gray and Black Officer uniforms, the simplest answer is this:
The “Black Officer Uniform” is worn ONLY by the Imperial Army for enlisted servicemen and junior officers.
The “Gray Officer Uniform” is worn by members of BOTH branches. In the Imperial Army only the highest ranking officers wear gray. In the Imperial Navy gray uniforms are worn by senior enlisted (Chiefs) and all officers.
But you said you didn’t want “Stupid answers or guessing” so here’s the details to back up my answer, explaining not only the meaning of the “officer uniforms” but the other uniforms as well…
Considering George Lucas based a lot of the Star Wars action sequences on the style of the old westerns and war movies he grew up with it is understandable that he would base the massive military space forces in Star Wars on the massive military forces of WWII and simplify things with two general branches: The Navy with its fleet of ships that exert control over vast territorial areas on land and sea (the ground and space in Star Wars’ case) and the Army with the troops and vehicles needed to exert specific control over the actual people and resources within that territory.
The two branches of the Imperial military work together in a coordinated joint effort and are much like the US military during WWII, except (in Star Wars’ case) the Marine Corps are not a separate branch, but rather an other specialized force incorporated within the Army, like the real-world Army Air Corp (what would later become the separate branch of the Air Force) which was a specialized force of the US Army.
THE IMPERIAL NAVY
Members of the Imperial Navy make up the crew personnel that operate and maintain the Empire's capital ships. Its purpose is similar to the real-world Navy (before the introduction of the aircraft carrier) and use its ships and their weapons to engage other ships, bombard fortifications, control access to/from the ground, protect/blockade commercial shipping, and transport ground forces.
THE IMPERIAL ARMY
Members of the Imperial Army make up the rest of the military and the majority of the forces: the troopers, vehicle drivers, and fighter pilots that fight “up-close-and-personal”. They would assume the roles similar to the combined real-world branches of the Army, Marines, and Air Force, plus the fighters from the Naval Air Commands.
THE UNIFORMS
There are basically 7 distinct uniforms shown in the movies. This does not include combat outfits like Stormtrooper armor, Biker Scout gear, AT-AT driver suits, AT-ST driver suits, TIE Pilot Flight suits, etc. With the novels, RPG’s, card games, and comics from the expanded universe many of the personnel seen in the movies have been given identities of their own. The original Star Wars card game provides plenty of examples for Imperial characters of different ranks, positions, duties, and shown in various uniforms.
A note about ranks…
Enlisted service members (and officers not in dress uniforms) do not have visible rank insignias in the movies. Ranks among officers is defined by a rank insignia of colored boxes placed on the left side of the chest when wearing their respective dress uniforms, and is further defined by the number of code cylinders carried in the chest pockets. For example a Lieutenant Commander and a Commander would have the same colored boxes on their rank insignia, but the Lieutenant Commander would have 1 code cylinder while the full Commander would have 2 code cylinders.
A note on items common to all uniforms…
BLACK BOOTS: A pair of sturdy boots are part of all the uniforms and the pant legs are always tucked into them. Most boots are around the mid-calf level and vary slightly in design based on the assigned duties. Personnel assigned to more rugged assignments (combat, mechanics, technicians, etc.) may have steel-toed versions with heavier soles.
BLACK SERVICEMAN’S BELT: The majority of uniforms for both branches have a standard wide belt with a large, flat (non-shiny) metal buckle. The belt could have a number of small metal cases on it. These “belt pouches” are used to hold small items such as tools, credit chips, rations, or personal belongings. In the movies there are Imperials with no belt pouches and the majority of them are shipboard, typically 1-2 belt pouches are seen. Gun belts are a modified version of the standard Serviceman’s Belt with a holster provided when issued a BlasTech DH-17 Blaster Pistol. It is the standard weapon carried by Imperial security guards, but also carried by personnel near the frontlines. The belt usually has 1-2 belt pouches (to hold extra ammo) but there are Imperials seen on Endor with as many as 4 belt pouches.
The non-combat outfits (in the basic order of appearance) are as follows:
UNIFORM 1: ARMY DRESS UNIFORM
Seen shortly after the capture of Princess Leia, worn by the officer that confronts Vader with the line “Holding her is dangerous. If word gets out it could generate sympathy for the rebellion in the senate.” In Episode 4, everyone in these uniforms are junior officers, the enlisted versions do not appear until Return of the Jedi.
What is most commonly identified as the “Black Officer Uniform” is actually the standard Army Dress Uniform for all junior officers and enlisted personnel. The all black uniform consist of a cap, double-breasted tunic, serviceman’s belt, trousers, boots, and regular gloves. Wearing gloves is not a requirement, some prefer to wear them while other do so only when needed.
Enlisted servicemen have plain tunics with no pockets or rank insignia. The tunics of junior army officers have a “colored blocks” rank insignia on the left side of the chest and two small thin pockets on the on the chest near the armpits. Depending on position, rank, and duty assignment the junior officer will carry 0 – 2 code cylinders in these small pockets.
The uniform is one of the outfits (the other is the Army Work Uniform) used by stormtroopers, AT-AT drivers, AT-ST drivers, and other personnel when they are not “on duty” or deployed in military operations and wearing their combat suits.
UNIFORM 2: NAVY DRESS UNIFORM (and COMMAND STAFF UNIFORM)
The “Gray Officers Uniform” appears with the first scenes aboard the Death Star. The briefing room scene is where several officers in gray uniforms are seen together. Though none of the officers are identified by name or rank (except Tarkin) in Episode 4, all of the officers in the scene are a mix of Navy and Army personnel. The two officers arguing at the beginning of the scene before Tarkin enters are identified in the story writing as Admiral Motti and General Tagge, a Navy officer and an Army officer, both wearing gray uniforms.
The uniform is identical in style and appearance to the Army Dress Uniform, the only difference is the cap, tunic, and trousers are medium gray color. It is worn by all high ranking officers from both branches, and all Naval servicemen of chief or higher. Navy enlisted servicemen below chief do not wear dress uniforms. Tarkin’s aide, Chief Bast, wears a gray uniform.
Since the uniform is seen worn by all high ranking officers from both services, this implies that senior officers are lumped together into a generalized group of “Command Staff” and are capable of leading large strategic operations involving both Navy and Army forces. An officer is responsible for the men and equipment under his command, he is therefore able to delegate orders to any of his subordinates regardless of branch to obtain military success. This occurs at all rank levels from the top down.
For example a General may charged with controlling a garrisoned planet and is responsible for maintaining order and protecting its resources. In addition to the garrison forces a handful of ships (2 Light cruisers and 6 Frigates) have been assigned to him. The Army General can order any Navy Captain under his command to have his ship patrol a particular zone within the star system. That Navy Captain can in turn deploy Tie Fighters and Stormtroopers to attack and board a ship suspected of smuggling.
As a side note… Grand Admirals wear a White Dress Uniform, this is established in the Timothy Zahn trilogy of novels with the character of Grand Admiral Thrawn.
UNIFORM 3: MILITARY INTELLIGENCE OFFICER’S UNIFORM
The first of these uniforms appear during the briefing room scene and is worn by Colonel Wullf Yularen, though (like the other officers) he has removed his cap. He is seated to the right of Admiral Motti, a.k.a. the officer that got choked by Vader after mocking the Force. The uniform can be seen again on two officers that walk past Chewbacca, Han, and Luke while they wait for the elevator that would take them to the detention center.
This uniform is nearly identical to the standard all black Army Dress Uniform, the only difference is the double-breasted tunic is a white-gray color. It is worn by officers assigned to Military Intelligence. Liaison officers, administrative assistants, and other junior staff members assigned to the Military Intelligence Office wear either the standard Army Dress Uniform above or the Army Work Uniform described below.
UNIFORM 4: NAVY HAZARDOUS DUTY UNIFORM
The uniform is worn by Navy personnel assigned to jobs that are more physically dangerous that the usual jobs done aboard ship. The outfit includes heavy gloves to protect the hands and a large helmet to protect the head and neck. Examples of this uniform appear in several scenes in the Death Star. The Navy Troopers are seen guarding the briefing room and detention center in Episode 4 and fighting on Endor. Technical crews in the Superlaser Control Room and firing chambers can be seen wearing this uniform in Episode 4 and again in Episode 6 operating the generator controls inside the bunker.
The uniform is nearly identical in appearance to the enlisted version of Army Dress Uniform (i.e. it has a plain tunic with no rank insignia or the code cylinder pockets) with a few differences. The most obvious difference is the very large samurai-style helmet, the sleeves are tucked into large black gloves that come to about the mid forearm, and it is made of more durable material than the Army Dress Uniform. Navy Troopers are issued a gun belt and normally carry the standard blaster pistol mention earlier, but may (as seen on Endor) be issued the same BlasTech E-11 rifle used by Stormtroopers.
There are two slight variants seen in the films. The less obvious difference is the Imperial insignias that appear on the shoulders of the Navy Troopers on Endor, the troopers and technical crews shown on the Death Star do not have shoulder insignias. The second variant is seen briefly (a second or two) during the destruction of Alderaan. At the beginning of the scene (just before Princess Leia is brought in) one of the console operators can be seen wearing gray version. It is the only one shown and was basis for the original Kenner “Death Squad Commander” action figure.
UNIFORM 5: TECHNICIAN’S WORK UNIFORM
Both services wear this style of uniform the only difference is the color of the cap worn, black for Army or gray for Navy . An example of the Army version is seen worn by the scanning crew that were ambushed on the Millennium Falcon in the Death Star hanger. Navy versions of the uniform can be seen in bridge scenes of the Star Destroyer Avenger when Captain Needa loses track of the Millennium Falcon in the asteroid field.
The uniform is a light gray jumper-style coverall tucked into black boots, with a black belt. Compared to the Dress Uniforms, it is more durable against wear-and-tear and its looser fit provide better freedom of movement for performing a lot of physical or dirty work assignments. The uniform has Imperial insignia patches on both shoulders, there are no colored rank insignias on these uniforms. They are worn by warrant officers and enlisted servicemen. There are two thin pockets on each of the upper arms (commonly used to hold small tools) and (depending on specialty) a data pad device is also on one of sleeves covering the forearm (usually the left) just below the elbow. This data pad is used in diagnostics and to reference technical databases when conducting repairs and maintenance.
UNIFORM 6: ARMY WORK UNIFORM
Technically this uniform appears in its modified forms as combat outfits (see below) in Episode 4, but its full unmodified form appears in Episode 5 in the scene where an Imperial Captain says “Good, our first catch of the day.” …just before his Star Destroyer gets blasted by the Ion Cannon on Hoth.
From a distance the uniform looks like (and is often mistaken for) the Army Dress Uniform because they are both all black uniforms with a black cap, but at a closer glance the uniform details clearly make them different. It is similar to the gray Technician’s Work Uniform except the jumper-style coverall is black and there are no pockets or data pad on the sleeves.
The Army Work Uniform and serves as an alternate option to the more formal Army Dress Uniform. It is favored over the Army Dress Uniform for “dirtier” assignments where freedom of movement and durability are more important than appearance. The Army Work Uniform serves as part of the combat outfits for Imperial Pilots and Gunners. Both jobs require personnel to quickly man their vehicles and weapon station during an alert. Both need only to grab their helmet and gloves and put them on to be ready as they make their way to their battle stations. Though in the case of pilots they must grab an extra item, the vest with the life support and environmental controls for their suit.
UNIFORM 7: NAVY WORK UNIFORM
The Navy Work Uniform appears in Episode 5 during bridge scenes on the Imperial Star Destroyers. It resembles the Technicians Work Uniform and is light gray in color, but (like the jumper-style coveralls on the Army Work Uniform) there are no pockets or data pad on the sleeves. This is the standrad uniform worn by all enlisted servicemen below Chief, though it is also worn by Chiefs and Warrant Officers (in place of the gray Navy Dress Uniform) when assigned to jobs where the formal uniform would be unsuitable. Ensigns and above do NOT wear this uniform. Unlike the Army Work Uniform, the Navy Work Uniform does not serve as a base for any combat outfit apprearing in the films.