As already mentioned before by other members, the short answer is lighter colors are cooler.
The more detailed answer is heat energy obeys the same laws of conservation as light energy. If a certain color reflects most light wavelengths (lighter colors like white), most heat energy will be reflected as well. Therefore, due to the nature of visual light, colors that reflect most wavelengths of light tend to be cooler than those that only reflect a few. Understanding how this principle applies to different colors can allow you to stay warmer or cooler simply by using different colored paints or fabrics and colors on your boat