The Pigmental Problem

"To blacken" means to turn black. "To redden" means to turn red. "To brown" means to turn brown, like with meat. And "to bleach" literally means to turn white, but we have a seldom used "to whiten" as well. I'll accept "to yellow," but Webster says that "to green" and other color words work, but I don't buy it. No one uses them very often. So I wonder why the first few are used more often, when plenty of stuff turns blue and green, like rotten meat and strangling victims. And why do only black and red take the suffix "en" when they become verbs? They don't seem any more deserving than green — "to greenen."