The light shed by Magica comes in a broad spectrum of colors. Red, green, blue, yellow, etc... none of which seems to effect output or ability. Many postulate that it has some kind of correlation to personality, or preferences, but even that does not hold up under scrutiny.
The one exception seems to be that certain "rare" colors seem to indicate extreme power and ability. White, for one, is only rumored to be a color magica can output.
But mostly it is mostly an interesting indicator of an individual, much like eye or hair color.
-On Magica and Wizardry, 11th edition