In the cartoon Ultra Magnus is blue and white and so are some of his toys. But I've also noticed Ultra Magnus being all white both his toys and in some of the comics but why is that? That always got me wondering.
Because the original toy Ultra Magnus had a white Optimus Prime as its cab and the classic UM look is essentially that white Optimus wearing its trailer as armor.
That's why you see white Optimus repaints called UM.
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SIDESWIPE: *grumbles* ... the greatest fighting machine in the universe and they make me a janitor!
I liked the notion that UM's armor actually regulates his persona. Without it he's a sociopathic killer. With it he's indefatigable and just. I think that's from some fanfic. When it was evident that MP-22 wasn't going to have the inner white Prime I was initially disappointed but now I prefer that Magnus is his own character. Leave the inner Optimus to the G1 toy and Diaclone PC.