Why Isn't Black a Color?

Color is based on human perception of the visual spectrum of light. Our ability to see different colors is due having a variety of cone cells on the retina that are sensitive to different wavelengths of light.

Black is the label we give to the perception of the absence of light reaching the eye. Objects that absorb all wavelengths of light, rather than reflect them, appear black. We also see black (or darkness) at night or when we shut off the lights.

When somebody says "black is not a color" they are referring to the fact that black is not a scientific observation of light. However, since color science is based on human perception, and our eyes perceive the absence of light, it is OK to call black a color.

Why Are Candles Made of Wax?

Well, one might argue that by definition we call a light source made of wax a "candle" (as opposed to an oil lamp or match which has a similar purpose but uses different materials).

But what is special about the wax in a candle?

To understand the mechanisms of how a wax candle burns, read Why doesn't candle wax burn without a wick? first.

Wax has several unique properties that make it an ideal material to be used as the "fuel" of a candle. It is solid at room temperature, which makes it easier to handle than liquid lamp oil which must be kept in a container. It is also malleable and melts at a low temperature, making it easy to shape into whatever form you want it to be. The low melting point is very important because the energy required to melt the wax must be less than what is generated burning it, or the flame would not be self-sustaining. Natural sources of waxes (such as beeswax and paraffin) are commonly available for use in candles.