As you probably already know, dark colors (black) will heat up more than light colors (white). Try using thermometer strips sold at pet stores (to stick on the insides of reptile cages to monitor temperature). They're cheap, don't break, are flat so you can put them under a piece of paper (if that's what material you're using) to check your temperatures. Try some materials with different reflective surfaces too (foil; shiny black vs.
