Thai black rice (also called black sticky rice or black glutinous rice) is a long grain, dark purple rice. When cooked, the grains stick together, and make a perfect base for this coconut rice pudding. It's usually available at Asian markets, but, if you can't get it, use any kind that's sticky. Fluffy rices won't really work very well. I like to use raw (turbinado) sugar in this, but white or brown will also work.