Just priming.

Priming of several figures.

Princess Leia gets grey primer, since she's almost completely dressed in white. The grey will work as an under coat AND as deeper shadows in the folds of her garment.

Superman gets primed white, since he has a lot of red and yellow to deal with. His outfit is "bright" compared to say Batman, so the lighter priming makes most of the work easier. I'll still have to "dark prime" his head and the blue bits of his suit, but the white won't hinder that.

Human Torch is basically all red, orange and yellow, so the bright undercoat is best.

Same goes for the "Imperial Guard" figures. They are dressed COMPLETELY in red, so they need bright undercoating too.