In general, we understand red birds thusly: the brighter the red, the better the bird. (Why? See this post.) The better the bird, the better his genes/parental care/mate, and the better his reproductive success.
But sometimes it’s more complex—and interesting—than that.
Red male House Finch. Photo by M. LaBarbera.
Yellow and orange male House Finches.
Photo by Ken-ichi Ueda.
Tough Little Birds 