If you're not going to be staying in extreme high temperatures I really don't think you should buy a MH based on color. Make sure the RV has suitable air conditioners for the size. Insulation is important as are double pane windows.
There are many, many dark color RVs out there and you don't really hear complaints about keeping cool - unless in extreme temperatures. I wouldn't peg Michigan as an extreme state. :) We lived there. If you're planning the summer in Florida or Arizona, Utah, deserts then that's extreme.
