Critical Angle your beam. This, of course, leaves you with the problem of how to separate the colors back out once your beam gets to where its going. One way to do this involves total internal reflection.
The index of refraction of glass isn't fixed; it's actually a function of frequency. Specifically, the index of the glass n and the angular frequency \omega of the light are related by n^(2)=1+(C)/(\omega _(0)^(2)-\omega ^(2)-C) where C=4.43e+32ra(d^(2))/(s^(2)) and \omega _(0)=2.9326e+16ra(d)/(s). Since different colors of light see different indices of refraction, different colors of light will have different critical angles.
angle =