Answer:
First, I have to explain something, just in case you don't know.
Color is determined by what parts of light an object reflects and which it absorbs.
Light is composed of three MAIN colors, blue, red, and green (the primary colors of light, not to be confused with the primary colors of pigment, which are blue, red and yellow). All colors are made up of a mixture of a certain amount of each of these colors. Yellow light, for example, is made up of 50% green light and 50% blue light.
Something that appears to be yellow, therefore, is absorbing the red light, and reflecting the green and blue light. Your eye sees the reflected light, so the object appears to be green.
Something that appears to be white reflects all light, something that appears to be black absorbs all light.
So something that is black is absorbing all light that hits it, and this light is turned into heat, which makes the black object heat up.
White objects reflect all light (or almost all), so they do not heat up nearly as quickly as black objects.