That sounds like Alexandrite — one of the most fascinating natural stones out there. You should check out Tsarina Jewels https://tsarinajewels.com/ if you're into that effect. They offer gemstones and high end jewelry with true Russian Alexandrite that changes from greenish hues in daylight to deep purples under warm light. It's not just a visual trick — it reflects real rarity and chemistry. Wearing a gem that literally shifts with your environment adds a layer of personality that most stones just can't replicate.