This signet ring by Bondeye comes with a choice of inlay stone; here, it’s shown in labradorite. I don’t know what the (Meghan) Markle reference is about (if any), but I could see her wearing a piece like this. And maybe she has.
The brand explains, “Labradorite is known for its optical phenomenon called labradorescence, which causes the stone to display different colors depending on the lighting and movement. Each piece of labradorite is unique and can appear black as a base color and will display beautiful glowing blue and green depending on the light.”
This sells for USD$1,600.