A loose interpretation of aura in Fan-Ball terms is a light-like soul-ish energy thing which can be used to channel magic, in a nutshell. I was thinking about this concept and wondered, what if there's more to color of a character's aura than just style? I've conjured up an idea for a game-like mechanic that incorporates aura magic.
In this model, characters with very different aura colors' magic is more powerful against each other, and similar colors are weaker against each other (sort of in the sense that objects of a certain color actually absorb opposite colors and reflect their own).
Let's say that the best magic damage multiplier you can have is 2x, and the worst is 0.25x. If we use these values, a formula for aura magic damage would look something like this:
R = Red Value
G = Green Value
B = Blue Value
c = color for designated character
abs = absolute value
Multiplier = (((abs(Rc1 - Rc2)) + (abs(Gc1 - Gc2)) + (abs(Bc1 - Bc2)) / 437) + 0.25
Okay, so let's do an example. Let's say we're calculating the damage multiplier for a character using pure yellow aura magic (RGB = <255, 255, 0>) and a character using pure cyan aura magic (RGB = <0, 255, 255>. Plugging in the values...
Multiplier = (((abs(255 - 0)) + (abs(255 - 255)) + (abs(0 - 255)) / 437) + 0.25
Multipler = ((255 + 0 + 255) / 437) + 0.25
Multipler = (500 / 437) + 0.25
Multipler = Roughly 1.4x
As you can see, the attack will be pretty effective, as the cyan and yellow in this case are both strong, pure versions of their respective hues, which are not too close on the color wheel.
Two colors similar in hue, such as Red vs. Orange, similar in saturation, such as two Greys, or similar in lightness, such as Light Blue vs. White, will not do very much damage against each other. The farther apart two colors are in terms of HSL, the more damage will be done.