I personally would prefer to see them make the choices that make the TOY looks good.
I'd happily forgo cartoon accurate white thighs if the chromed thighs make it look a lot better. Likewise, I'd skip a red bumper if they had gone for a chomed one.
Optimus mightn't have ever had metallic blue eyes, but I don't care about that. The toy's eyes are blue and have got bling! That's a heap better than sky blue generic eyes.
I think a good example is
Mattel's Voltron. The coluors are flat and the lion Legs are white. It's pretty cartoon accurate.
But the colours don't look half as nice as
This version which takes cues from the original toys as well as the show. Hell, even the
Masterpiece version looks nicer with the chrome bits. As long as the TOY looks good, I'm fine with that. I'd hate to have a series of Masterpieces that are large, bland, flat coloured toys based completely on the cartoon, because as Gok said, they wouldn't feel like masterpieces.