Each of these three directions has a strongly different absorption spectrum, causing different colours to be seen when viewed from different directions in relation to the crystal structure, an effect known as pleochroism. Daylight contains high proportions of blue light, tungsten lighting contains a higher balance of red light. The two main optical directions of alexandrite absorb light of different wavelengths in considerably different ways. If this sounds technical and complicated, it is because it is technical and complicated. I will try to return to this paragraph later when I have worked out a simpler sounding way to explain the phenomenon.
Any suggestions welcome.
There have been many simulated alexandrites produced, usually made of synthetic corundum, occasionally synthetic spinel. A Japanese company also markets a synthetic alexandrite. If real they would weigh about 5 to 10 carats each, and would be worth between about 5,000 to 20,000. As dress rings they were probably sold at under 100. Strangely enough, I believe that when they were originally sold, most of them were probably described by the jeweller as alexandrites.