I just bought a ring. The stone on it is purple in the sun and blue in the yellow light. What kind of stone is this?

Common ones that can change color are variable stone and sapphire.

The color you said is the same as the color-changing sapphire image.

However, it can be seen that color-changing sapphires are generally synthetic.

What you said is purple under the light, and the composite color is usually dark blue. Yours may be true.

According to your description, it may be a priceless opal.