Thanks for posting your strand. It's not possible to be sure from a photo but I'd guess that your beads are natural turquoise.

I don't see any tell-tale puddles of plastic filling the crevices. Neither do I see darkening in the crevices typical of shoe polish or other "enhanced matrix" tricks.
Some stones appear to have absorbed body oils and deepened in color.
Most are a light blue typical of mid grade stone.

Turquoise has been enhanced for a long time. Early on with grease & oils, later with wax and colored wax. Sometime in the 50's resin or epoxy was first used to stabilize turquoise.

I don't remember when shell workers in the Philippines began to make heishi to supply the US market. I suspect the shell heishi on your necklace is from the Philippines rather than being made at Santo Domingo Pueblo.