Resin gland color, potency, and type of high
Gland color will vary with ripeness of the individual THC glands, starting at clear, turning to milky, then turning to an amber color. There may be some exceptions, such as some of the Blue strains and Blackberry. These will have darker, sometimes purple gland heads. But by far and large, these three steps of ripeness will exist with the vast majority of strains on the market. The first stage, clear, will tend to make for a more cerebral, up high, with very little body effect. Harvesting at this stage when little if any trichomes are milky yet, can be tricky. Harvesting too early can make for a beautiful plant that will not have much psychoactive capability! THC needs to "mature" to be able to pass its psychoactive capabilities down to the smoker. This is why I always recommend waiting until 50% of the trichomes hit the second stage: milky or creamy. At this point, you will definitely have a plant which has reached its genetic potential.
The milky trichomes have some "cerebral" qualities, as well as some of the more "physical" characteristics of the high. The last stage, amber, brings on a more sedative, physical stone. If this is what you're looking for, than I would recommend a sativa/indica cross, or an indica dominant plant. Amber trichomes seem to ruin a sativa high if the plant goes too long.