lens - Why aren't more lenses white?

So high end Canon lenses are white. This is to reduce heat, correct? If so why is this something that only appears in really high end Canon lenses. I wouldn't think that painting a lens white increases production costs in any measurable way, why don't all lenses (and maybe by extension DSLR bodies) come in white, or at least have the option of buying them in some off-white color?