If you're using halides by themselves here is a little comparison:

6500k - Yellow coloration but the "BEST" coral growth and most corals will turn yellow or brown
10k - Crisp white w/ good color growth and moderate coloration in corals
12k-15k - Hint of blue w/ moderately good coral growth and good coloration
20k - Very blue w/ slow coral growth but excellent coloration

Bulbs will vary in color depending on manufacturer and ballast.

If you want a top notch fixture for you tank you should check out ebay, RC, R2R, and NR. I've seen a few 150w Sfiligoi and Geisemann units go up for sale in the past 2 months. People tend to be shying away from halides because of the price of bulbs, wattage consumption, and heat transfer, and offering up top dollar fixtures for cheap. Just last month I was thinking of purchasing a Geisemann 150w unit that was on ebay that sold for around $130 and it was relisted 2 or 3 times.