Dark colors absorb heat while light colors reflect it. Once you have figured out how to maintain the best temperature, you need to find the best spot. Bats prefer an unobstructed area so that other animals like squirrels and raccoons do not bother them. Bats are migratory and should begin arriving around early summer. Experiments show that if you put your house up in the fall or winter, it will more likely be occupied.
Bats usually stay around till fall.
To observe the bats, shine a flashlight into the open bottom. After awhile they become pretty tolerant of this. They do not like it when you touch either the mounting pole or the house. If you are observant, you will see the bats flying in the area at dusk. You might want to try looking at them with binoculars since in flight they look very similar to birds.