This paragraph is going to be somewhat nerdy, I apologize, let's sit back and discuss light. White light, like from the sun, is composed of all colors. Additionally, different colors absorb different parts of the electromagnetic spectrum. The colors that we see are what is reflected not absorbed by the material. For example a red block would absorb all the colors except red, red light is reflected back.
White objects reflect all light and black objects absorb all light.
The last piece to this story is that light is also energy. Red, yellow and orange colors contain less energy than the darker colors. Unless you are testing your deodorant. The students' experiment is simply to place a set of the blocks outside in the dry valley and a set outside in Hanover, New Hampshire. Then a comparison could be made between the amounts of energy each block absorbs.