Hi,
I have 2x400-watt 10 000K MH's, 1x150-watt 10 000K MH's, and a 40-watt actinic. They 10 000K are almost a perfect white, just a hint of blue which gives the fish a lovely shimmer. When I replace the bulbs next time I may go with 12 000K just to see what they are like, and because I like a blue sheen to my tank. However, the German 10 000K's are a beautiful colour and seem to be excellent for coral growth.
Regards,
Tom