Another thing that one must consider when getting lights is the spectrum of lights that you are going to use. There are an assortment of "flavors" to consider here. They range from 6,400Kelvin(K) to 20,000Kelvin(K). While yes at a lower spectrum, such as 6,500kthe corals have been found to grow more rapidly then at 20,000k the coloration will look quite different, and sometimes like a whole other coral.
Trying to achieve as many spectrums is the best way to keep healthy corals. While yes the colors are more vivid under blue lights, like the 20,000k, they are still not as health as they would be if they were getting 10,000k(white) plus 20,000k. With the broken up spectrums, it adds more ranges to the light given off and therefore, adds to the health of the coral.
There are endless combinations you can use to break spectrums down. Such and such blub, with such and such, ballist, with such and such reflectors... the combinations are almost endless. One of the best methods for finding a cororation you like is to use suplimentation. Useing, for instance over a 55g SPS reef, 2x175w 10k MH. This written out is: 2 175 watts 10,000Kelvin Metal Halides. The 10k are going to be white and will allow the corals good lighting to grow. It gives sufficient PAR(photosynthetically Active Radiation) to grow at a good pace, but what it laks is the spectrum for coloration.
You will want to Supplement the lack of coloration by using another bulb or two. Many still use PC, lighting, wihle other use VHO, and now people are moving toward T5's. The important thing here is to get as much as you can out of the bulbs. If you are using PC lights you'll need enough to get 350watts over the tank You'll find using something like Coral Life fixtures to be bulky and will even block some of your MH. You do have the option of using Retro kits for this as well so don't fret. If you use VHO's it's easily achived and the same goes for T5's. Though you can achive healthy corals without matching the original lighting, the 50/50 lighting it is optimal. The bulbs you will be using will be called TrueActinics or 20k.
To each his own. You'll find that using differnet bulbs will hold a different affect on corals, but by supplimenting, you'll find your corals look like a different coral all together, the'll be in better health, and will grow, unlike if you were to use just Blue lights.
For an intro to lighitng please see Coral Lighting and Acclimation