Such an effect is called pleochroism, and crystals which show variations in their colour when viewed from different angles, or by transmitted light, are called pleochroic, or pleochromatic-from two Greek words signifying "to colour more."
"The Chemistry, Properties and Tests of Precious Stones"
John Mastin
pleochroic Haloes is a popular exposition of an inconspicuous but very beautiful phenomenon of the rocks.
"The Birth-Time of the World and Other Scientific Essays"
J. (John) Joly
The descriptive name "pleochroic Halo" has originated from this fact.
"The Birth-Time of the World and Other Scientific Essays"
J. (John) Joly