Light Lab
Turn the room lights down and rake a slit of light across the table. Every ray carries one wavelength, bends by that wavelength's refractive index, and fades inside colored glass by that wavelength's absorption. The colors you see are the sum of a million such rays.
Drag the glass. A model: light in one plane, each ray one wavelength, Fresnel reflection averaged over polarization, refractive index from SCHOTT Sellmeier fits (Zemax catalog 2017-01-20b, via refractiveindex.info), absorption from the page's illustrative colorant spectra.
Two things to try. With the dense flint prism, the white beam fans into a spectrum, because the index falls from 1.83 at 420 nm to 1.77 at 700 nm. With crown glass the fan is about a quarter as wide (its index falls only from 1.528 to 1.513). Then give the prism cobalt and drag it up and down: light crossing the thin apex keeps more red than light crossing the thick base, because absorption grows with path length. The glass has no single color; each ray's color depends on how far it traveled through it.