HDMI standard: Color depth = 1
No, there is not a HDMI format defined for black/white images. The video section is compatible with DVI-D. This was specified to replace the analog VGA signals, which had the same bandwidth no matter whether black-and-white or colored (in fact, B/W may be argued to have more high-frequency content :-)

However, I use a 35 foot HDMI cable from my receiver to my TV, and it works; I've seen people do 75 feet by putting a HDMI amplifier in the middle.