This black/red skin colour is absolutely brilliant. It’s strong and effective enough to tie all the members of the unit together even if you add all the colours of the rainbow on the detail parts. This is a really good idea ! The red lines on black background have a strong gaphic effect which is really classy. All your units have their own identity.
I had not really thought about it that way to be honest but you are right, the strong red/black does help to integrate the colours! I am a big fan or reds and blacks. I always liked Bryan Ansells Chaos Marauder Cavalry unit. 😉