When you where dark clothing it attracts the sun rays more then a light colored shirt would, therefore dark clothing will make it hotter when the suns out.
different colors effect temperature in many ways, they tend to absorb more or less amounts of heat. in example you water be more warm wearing a black shirt on a hot day then a white shirt.
Color effects temperature because light is absorbed and reflected based on an object's surface color, black absorbes more heat because it is a darker color and has less albedo (closer to 0) unlike...