After painting my Ratchet's head red-with-a-white-chevron to mirror his colors as seen in the old Marvel Comics, I figgered it was a matter of time before I paint Megatron's to match. Like Ratchet, Megatron had a differently-colored character model than the animation, mostly because the comic was an earlier creation and was shoved out the door before things were finalized. One result was that Megatron had a black helmet (and yellow eyes) rather than the all-silver look.
Since Classics Megatron is supposed to represent his Marvel Comics iteration, so why not blacken up his head? It also helped that his toy has severely yellowed in the two or so years I've owned him. Those peach-ish looking bits on his cannon and shoulder were originally bright flourescent orange! The tops of his shoulders and head were also showing signs of yellowing. You can't see them from this angle, and the new paint on the head covered up the yellowing there.
I do wonder how this toy would look in a full-body redeco based on the Marvel Comics colors, with the red midsection and what-have-you, but I like the colors as-is, really. Well, minus the yellowing. I think the purple, green, and orange suits him, just as it suits the toy history of the character.
But to me, Megatron's helmet should be black. I think it looks better since being mostly all silver is kind of boring, and I think it helps makes him look more evil. I wouldn't mind a black face inside a silver helmet, either, as what I'm really after is some more contrast.