Just want to add my 2 cents here.
White is white because the farmer ties the leaves over the head to keep photosynthesis from happening.
When it is opened, the first color in the process is purple.
Actually, regarding veggies, in Germany asparagus is grown under earth cover. If the head starts erupting, it turns purple and is sold as second grade.
While the above paragraph has no bearing on the cauliflower, I just think it's an interesting tidbit.