What will happen if you got laser hair removal on light colored hair?

No or less result: Laser targets at the melanin inside of hair follicles. If you have light colored hair, laser hair removal is not gonna work well.

Typically, not much: Laser hair removal works by heating up the cells in the hair follicle enough to damage them. In order to damage the hair follicle without damaging the surrounding skin, the laser energy must be absorbed more by the follicle than by the skin. This will only happen if there is a contrast in color between the hair and the skin. Light-colored hair is too similar in color to the surrounding skin.