My birthday is in June, whose birthstone is generally currently listed as Alexandrite (it has been diamond and pearl in previous eras, however).
Alexandrite changes colors in different lights. I have several Alexandrite pieces, including one white and one gold ring (the white is shown in the photo). It has become my favorite stone because I am so many "different people" and the ring complements that concept.
This particular stone, lab-created, changes from dark to light purple, to black, to clear with speckles, to intense dark green, and maybe shades I'm forgetting in-between, too--all depending on the amount and type of ambient light (fluorescent, sun, incandescent, LED, firelight). The photo above was taken without flash in low incandescent light.
I just love the dynamic of this stone, changing colors to match its surroundings! That's exactly what I try to do--adapt to changing conditions in life. This stone speaks to me.
If you've never been familiar with Alexandrite, don't worry. Non-lab-created Alexandrite almost all comes from Russia. Under the USSR it was considered VERY illegal to export because it was a national treasure (according to Russian friends of mine). So, almost all Alex. you see is lab-created, therefore flawless and more affordable than many natural stones like rubies or emeralds.
Some lab-created stones have very little color change, however, and look pale pink almost always--be sure to check it in various lights before buying Alex. A good salesperson will insist on this--showing off the main feature of this unique stone (I don't know of any other stone that, under standard lighting conditions (non-UV light source), change colors this dramatically and COMPLETELY).
If you're a chameleon or curious, ask to see the Alexandrite pieces at your local jewelry store and be sure to see the color change under different lights: you may not be able to recognize it just by walking past the displays, and it is still very rare and not a big seller for most stores because people assume it is simply another type of stone based on whatever color it currently is (amethyst, emerald, etc.).
Anyway, that's why Alexandrite is the perfect birthstone for me and why I love it so much. Hopefully I've inspired someone to look at it in person, too, and also perhaps fall in love with it. Cheers!