A 10K MH bulb without a "stong" actinic supplement, the color of corals can look very washed out.
My 70W 10K Ushio MH bulb was very crisp white looking (not yellow at all), but I only had 55W PC actinic bulb with it, and all the corals looked washed out. Blue mushrooms came out blue and not purple, and yellow polyps were looking bright yellow, but all the other colors did not look pretty to me. I bet that the colors would have looked very nice under the same bulb if I had another actinic PC or VHO bulb with it. I feel that PC actinic bulbs do not bring out colors like VHO acinic bulbs can, though.
Tomoko