Color Change Garnets.
Garnet members of the pyrope-spessartine solid-solution series from Bekily in Madagascar display several colors depending on the light source. The alexandrite-like color change from blue-green in daylight to purple in incandescent light is mainly caused by relatively high amounts of vanadium. Although they look a lot like alexandrites they are different because they change color throughout the day. They are green or blue grey in the early morning and reddish in the late afternoon or in strong sunlight. Bekily garnets will appear red in the afternoon while the alexandrites remain green. Garnets from other parts of East Africa also change color but as they normally change from brown or orange to red, they don't look much like alexandrite.
Some of the stones are almost blue especially under fluorescent light but most of them are grey blue or green in daylight and change to red under incandescent or late afternoon light. The stones can show an excellent color change and can easily be confused with alexandrite.