The uniform colors have been debated for some time.
I agree with the "dress" uniforms being the colors as suggested by the sunburst (above). I've wondered what this would do with the sunbursts themselves, such as maroon sunburst upon....a maroon uniform. There would have to be some other color behind the maroon sunburst to make it visible on the maroon dress uniform. Perhaps in dress uniform, a white sunburst is used in all services since the uniform itself already denotes branch.
As for fiield uniforms, I think this would be by utility. Army uses black in dress, perhaps some sort of camo in the field. Marines would have another consideration. Their armor may or does (according to which source) have a chameleon option. This means the armor is going to be a different color based upon what enviroment they are in. Green, tan, white, etc, etc, with the maroon sunburst upon the breast and/or helm. So what does the armor look like when chameleon isn't being used? I always imagined white due to a nature of the chameleon armor itself (technologically it might be easier to "paint" on a base white armor). So, when not in a threat environment, the Marines walk around in completely white armor except for the maroon sunburst. There have been a few graphical depictions that show Marines in white armor. Others my prefer that the base color on the armor is maroon when chameleon isn't activated.
Thus, if I had a large collection of Imperial Marines, I would personally paint some white (or maroon), others in some sort of common field color such as camo, green, or tan for when chameleon is activated.
