In spite of colours own refractive index, how does the angle and slanting surface of prism effects dispersion?

I'll asume here this question is about some lapidary subject or about a particular mineral specimen and so I'll give you a couple of examples that apply to that example, IE: in the Feldspar family I'll choose "labradorite".....and I'll be more specific and pic a type, "Blue Speckled labradorite with Yellow flashing"...there are two particular plane crossings are much les than 45 degrees that are blue which crosss in a similar direction and one plane that crosses in an opposing direction that's two directions IE;two going left to right and one coming at you, the bottom plane being further away and the top of that plane being closer......depending on how you polish that specimen, and how you look at it in sunlight, you'll see two blue shades or even four due to mixing of shades of blue, then turning it slightly to the right to show the yellow? it will be greenish with blue speckles. Then turn that rock sideways, look at it again and it appears yellow, turn that slightly sideways and it again appears yellowisg green with bluish speckles...........But, you can do that with stones like opal, Onyx, Tiger's eye and about 50 more types of minerals.........hope that helps.