>>10658530Hard to pick, I always lean toward red though because red+green is one of my favourite color combos. Fell in love with the first time I saw Levahk.
If you're talking specifically mata heads then I think the Red+blue combo Makotey had going on was really striking.
>>10658657They're not supposed to be removeable but there's a few tricks to force them back out. The brain piece connect to the skull by having the eyes basically clip around the nose, so what I like to do is just wedge something into the top of the head (like a spudger or a guitar pick, maybe a screwdriver but that'll chew up the plastic) to work that clip loose until it can be pulled out fully.
Some people like to put something into the brain's axle connection and then push it out by putting an axle through the mouth to force it out, but I think that puts way too much force on the clip.