In a real military, there is a WIDE VARIETY of different uniforms in use at any one time. It would be interesting to see this variety. The only time we saw anything remotely like this was in Generations.
The US Army has 3 standard uniforms. The A (uniform with jacket), B (uniform, no jacket) and the ACU (camoflage)
Then you have assorted jump and flight suits. And it isn't as if you can pick whichever uniform you want for the day. Base commanders usually decide which uniform will be worn, and that depends on the type of work involved. Most bases go with the camos while the Pentagon - along with more clerical personnel - goes with either the A or B depending on the weather.