At least some of the Muscovite infantry (e.g. streltsi) had rather colorful uniforms
. I find this series of articles from Airfix Magazine
(also published as a book) quite helpful. Also, there are of course the ubiquitous Ospreys, provided you realize the color plates are just artist's impressions and concentrate on the text instead. I'm sure someone will claim every single available source in English is wrong, but that is IMHO not very helpful (one bad source is better than none, as it enables you to put painted figures on the table).
My own rule of thumb is that if the figures are sculpted in uniformly cut clothing, it looks silly to paint them in totally random colors (did the regimental tailor run out of cloth?). I'm also prepared to sacrifice some historical accuracy for playability – I've found when introducing the game to new players they have a hard time keeping track of the various units, especially when the names are totally incomprehensible. So I paint my reiters in red uniforms while keeping the boyars and servant cossacts random: