Hmmm....
A few comments... I started this thread half in jest (and surprise that I'd be running a classic-era game), but as always some interesting (and amusing) replies.
With regard to the two uniform styles worn in Generations, it is actually very similar to the uniform styles worn by naval officers of the US navy. A whole bunch of different styles.
- You've got your whites. Kinda like a white jacket or shirt (long or short sleeved) and white trousers (for men) and a white blouse and white skirt for women. Rank insignia is given on the shoulder boards in the form of stripes.
- Khakis - The more casual duty uniform, khaki shirt and trousers/skirt, with rank insignia given as a pin on the collars.
- Blues - Dress uniform, blue jacket. trousers/skirt, white shirt, tie. Rank insignia in the form of stripes at the wrist. Also got your summer blues, which gives you a white shirt instead of the jacket, rank insignia at the shoulderboards.
In TNG, I'd view the TNG uniform as your whites, the early DS9 as the Khakis and the dress uniform as the Blues.
Around First Contact, I'd say you got rid of the DS9/VGR style uniform as the Khakis and replaced them with the First Contact style. Also a new sort of dress uniform (as seen in Insurrection) as blues. However, if you look closely, you can still see the season 3 TNG uniform in DS9 season seven, so the "Whites" are still present, just rarely used (makes sense for a war).
For TOS, I'd say you only have two uniforms, the normal ones and the dress ones.
For TMP, if you look closely, there is tremendous variation in the uniforms - from Kirk at the start (I'd put that as Blues). You then have full jumpsuits ("khakis"), and shirt and pants ("whites"). I don't think the TOS style uniforms would still be around.