Thank you for the answer!
I searched the forum and "10 bit color" results did not answer the question.
I have ATI Radeon Sapphire Vapor-X HD 4870 1GB card installed with HDMI output (no DisplayPort).
But I do not have "enable 10 bit pixel format support" checkbox in my Catalyst (ver 12.10 x64 Win7).
Does this graphic card allow to use 30 bit color output?