The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar".  Ordinary chrysoberyl is light to medium yellow to yellowish-green, grayish green, brown to yellowish brown; Transparent to translucent.

Cat's eye Chrysoberyl

Cymophane is popularly known as "cat's eye". This variety exhibits pleasing chatoyancy or opalescence that reminds one of the eye of a cat
In this variety, microscopic tubelike cavities or needle-like inclusions[ of rutile occur in an orientation parallel to the c-axis, producing a chatoyant effect visible as a single ray of light passing across the crystal.
An alexandrite cat's eye is a chrysoberyl cat's eye that changes color. "Milk and honey" is a term commonly used to describe the color of the best cat's eyes. The effect refers to the sharp milky ray of white light normally crossing the cabochon as a center line along its length and overlying the honey-colored background.]

Color types for Color-Change Alexandrite.

A brief description of the color types for Color-Change Alexandrite used at AGL Thai Laboratory Gemology.

Alexandrite

The alexandrite variety displays a color change (alexandrite effect) dependent upon the nature of ambient lighting. Alexandrite effect is the phenomenon of an observed color change from greenish to reddish, orange or brownish red to purple red and also brown to reddish brown with a change in source illumination.