Plants do not use heat to make their food. Instead, they convert light energy into useful chemical energy. It turns out that the pigments (called "chlorophyll" molecules) that are responsible for harvesting light energy from the sun are green in color. These chlorophyll molecules absorb light from the sun and transfer this energy by "bouncing" electrons around the chloroplast, which is the organelle that houses chlorophyll molecules. The chloroplast uses the "movement" of the electron to generate a chemical called "ATP," which the plant uses as a source of energy.

Plants don't absorb heat; they absorb light. Specifically, they absorb blue light and red light, but not green light.

Ironically, the largest part of the sun's energy comes out as green light. Why plants don't use it instead of the less common blue and red I don't know.

You´re correct that black color absorbs the most light and reflects the least light, and white color reflects the most light so it absorbs the least. When we talk about what we see we are actually talking about reflection, the opposite of absorption. Plants reflect green light - this is why we `see´ them as green. Plants actually use much of the light spectrum, particularly red and blue light. These colors are then absorbed by the plant. But plants do not use green light, so they reflect it back and we see green!

There were some recently posted Youtube videos which answer this question: