Well, basically my dad went to the trouble of making me a very nice hardwood display cage with built-in incandescent lighting, and imperfect as it may be (see the elastics holding the latches down?) I feel obliged to use it. If I were to turn on all nine lights (three on each level), it would be way too warm for the black milks, although the Sinaloan who lives on the top level would probably be quite happy. There's usually a month or two in the summer where it gets warm enough that I have to disable the lights entirely to keep the cages cool enough for the black milks. In fall and spring, the temps are just about right using one light per level, and in the winter, I use a heating pad under the top level as well, just to keep the Sinaloan toasty. Although the gaigeae spend most of their time on the cool side of the cage, they will frequently bask under the light as well, especially right after a meal, or just before defecating or shedding. Until they were almost 3 years old, though, my breeding pair of black milks lived in unheated 10-gallon aquariums, the same ones that now hold my two unsold yearlings. The 7 surviving '06 hatchlings now inhabit the Sterilite shoeboxes that the '05s recenly vacated, which are all also unheated.
Whew! Anyway, I guess the long and short of it is that black milks do fine in an unheated cage at room temp, but if you want to set up a temperature gradient, as long as the warm side is no more than 85 degrees, and the cool side is no more than 75 degrees, they will do just fine.
Nate