You're correct, Wicca24: Magic has no color. Some people have decided to describe certain aspects of some things by using color names, but some things are not as concrete as being absolutely good or absolutely evil, which is generally the attempt at calling something white or black, respectively. Some may call everything in the so-called middle grey.
There may also be some out there who decide to assign a color based on some aspect of their tradition, such as a natural witch (someone who uses nature -- in the sense of being among the trees and out-of-doors -- in their practice) may choose to say they use "green" magic. Some may use "blue" for water-related practices, or some other aspect. Or some color may be chosen to represent a principle aspect. But ultimately it is up to the practitioner and the tradition they follow.