Ruby.

Polarized Spectra of ruby in a zoisite-ruby section (origin Tanzania)

Pictures above and spectra show the pleochroism of the ruby crystals, deep pink to pale pink due to the intensity change in the absorption  band at 550 mn. The green curve is an amplified higher resolution recording of the small band near 700 mn.

The zoisite is also pleochroic from blue-green to green to yellow.