Either way the surface will heat up in direct sunlight, even if the air temperature isn't all that high. The lighter color you can make the deck, the cooler it will be - or if you position a deck umbrella or two strategically you can shade some of the regular walking area during the peak sun midday hours. If you want to compare the deck to bare cedar, I would buy a cedar deck plank and compare the temperature before you go and strip the paint off!