Go with the MH. You're right about the color of the mercury lamp. The pulse start MH system that killnernoodle is using is about the best you can get right now. Use an open fixure rated lamp if you can so you don't have to shield it in case of the rare explosion when the lamp reaches the end of its life.
From the
Venture Lamp Brochure:
Venture's open rated MP and MPI lamps contain protective quartz shrouds which helps contain hot particles in the lamp in the event of an arc tube rupture.