Cuprum will no doubt be along later to give more detailed information (and point out my errors

), but the basics of interwar uniforms are that they are quite close to RCW/WWI era-uniforms except they have a turned-down collar and enlisted ranks should have the side cap, and
not the earlier peaked cap. Epaulettes/shoulder boards still do not reappear in the Russian army until WWII and the only rank indication is collar tabs, though officers have sleeve insignia as well.
Insignia colours for service branch do match WWII and infantry uniforms are the WWII mustard khaki in overall colour (with high degrees of variation due to a large variety of origins). There's a lot of colour variation in officers and other service branches. For instance, infantry officers often have the wider deep blue riding trousers, armoured troops have a kind of pale blue-purple grey uniform, etc. Politruks have the deep blue pants of officers, but would wear black leather coats. Hats and hat bands for officers also have a large number of colours.
Also note that there are technically no "officers". At this stage, Russian ranks still retained a purely functional meaning "platoon commander" and not "lieutenant" or poruchik/sub-poruchik.
Here are some interwar Russians I did, mostly using Copplestone's RCW soviets as a base (they have the standing collars, but it's hard to tell, so I just fudged it) with West Wind side cap heads for the infantry (note how much my khaki varies):

(left to right: Infantryman, medic, platoon commander, infantry scout (with non-standard hat), infantryman)

(left to right: deliberately ambiguous figure who could be a lower-ranking officer or a uniformed civil official, WWII infantryman (I needed filler and he was the only one that worked), infantryman)
And some "characters"

(left to right: Politruk, civilian, hero, captain of armoured forces (with non-standard coat and boots), aircraft mechanic)
No doubt there are errors and shortcuts, but this gives you a very general idea.