When we were buying riot gear for our QRF unit in Panama, we purposely chose black because it was intimidating. The gear is there to protect you if you need it, but if you can intimidate the crowd enough you can avoid violence (though I used some very out of the box tactics to defuse a crowd with cheap hot dogs and KoolAid instead of intimidation when possible).
So, from that perspective, you will want to pick a color scheme that the mob/crowd will be intimidated by. Maybe 'cultural' influences that make a certain scheme more intimidating in your imagi-nation. Maybe a deep red so blood does not show. Maybe green is known to anger the 'cause' of the mob/crowd so the riot cops intentionally wear green to entice confrontation. Maybe the cop HQ/Admin types have been dealing with replacing expensive pilfered 'cool black' uniforms/armor so got the latest batch in pink to decrease the desire to snag a set.