You want to see what a real beret looks like? Here you go:
http://www.answers.com/topic/chasseurs-alpins
Now THAT´s a beret

(for info: these are "chasseurs alpins", french mountain commandos; sorry to badger you with french troops, but they´re the only ones I know). And no, I wouldn´t want to have to wear one of these either.
Seriously though:
for scouts I´d only take standard issue fatigues or flight suits and possibly unit and rank insignia (but that one´s optional). Otherwise I´d allow a little creative latitude for the "accessories" (underarm gun holsters, various headgears etc.).
For regular troops: take your pick, depending on what "nationality" (like Darrians, Regency troops, Regular third imperium etc.), unit type (infantry, wet navy, space navy, marines, special ops, whatever), unit (there might be small differences in uniform from unit to unit, like different badges, some units wearing distinctive signs like decorative weapons, etc.).
My suggestion for standard base colouring:
Brown, khaki or green for army
White for space and wet navy
Black for space marines (do they need a uniform? just put´em in TL 12 battledress and point them in the right direction

)
Blue for planetary air forces/SDB units.
Oh, and of course a black bodysleeve with individual extras for Star Vikings (just in case you want to try TNE

).