Beyondthe, the entrances are cut small on these boxes, and with the cover on it gives another 3/4 x 1/4" (18 x 6mm) entrance. I wanted to keep birds, mice, etc. out of them. Like you say, the dark colors just absorb the sunlight. I didn't want rain blowing or running in through the hole I cut for ventilation, and I was reminded of the vents we put on metal shipping containers to take care of humidity (Believe it or not, 20 x 8 x 8ft [6 x 2.3 x 2.3m] is vented with 12 - 3/8" [9mm] holes).