[cma22inc]

During the time of the crusades the armor of the day would have been chainmaile and not plate armor. The chainmaile breaths much better and does not retain heat like the plate armor does.

I would image they wore light colors (white) as well to reflect heat and cotton undergarments which once soaked with sweat would wick heat away.

I'd say they had a very rough go of it in the middle east in direct sunlight.