Greener the better?

The actual color of the trichomes doesn't have much to do with it; the trichomes arejust off-white and a little yellowish sometimes. The various color hairs also vary greatly in number and color, and regardless of the color, the more hairs and crystals, the better.

Indica is darker buds, and sativa is also lighter, and more "neon" green. In this sense, the color can be indicative of the nature of the high, but not much further.

Also, indicas smell darker; you get weird scents like chocolate, hash, and cherries in indicas, whereas sativas can smell anywhere from fruity to lemony to earthy to almost like chamomile tea.

Resin glands and hairs are usually a good sign because they indicate that the plant had ample nutrients and had excess energy to expend, both on producing the glands/hairs and on producing more THC. I've heard mixed reports as to whether the resin glands themselves have high concentrations of THC; I suspect that it varies by strain, with some strains (such as those grown to be used to make hash) having THC-rich resin and others (probably including most strains) having resin that contains mostly other cannabinoids. I'm pretty sure I read somewhere that scientific studies have shown no correlatin between resin glands and potency when compared to less resin-heavy plants that had equal access to water, light and nutrients; however, as I said, the presence of lots of resin indicates favourable growing conditions, so in practice, resin glands are a good sign whether there's a lot of THC in them or not.

As for colours, I doubt there's any genetic correlation between darkness of the bud and amount of THC (although I could be wrong). A more likely explanation for any observed correlation is that a majority of the good strains in your area happen to have darker buds. The best I've ever smoked was pretty average in colour, but covered in resin glands.