If I keep female rainbow fish and male rainbowfish together will the male color up more
I think so. Most males are known to be more colourful.
Yes & no.
With a group of just males, they will spar and display their colors to establish dominance.
But with rainbows their best colors are shown in the morning hours while they are spawning, and that can only happen with females present.
For this video I removed the other males and all the females. They were quite aggressive and towards the end of the session there were a few torn up fins. Adding the others back settled things down again.