Sterling Box-Set Multi-Colored Stone: What May It Be?

The stone is nearly square, with gently rounded sides; it's ~3/8" at the girdle, an ~1/4" deep, an' all facets are roughly square; quilted? Under UV light, it becomes almost clear. In intense incandescent light, when tilted slightly or rotated under the lamp, it shows a range of shades; greens, blues, purples, an' occasionally a flash of orange...perhaps others I cannot easily name.
I'm afraid to hope it could be alexandrite...but have no knowledge that will allow me to confirm or deny that supposition. The setting is marked 925, with a deep concave (but empty) dot immediately beneath that; the bale is also similarly stamped. The overall impression is of quality, based as much on the strongly designed but somewhat open an' airy setting as the (to me) unusually attractive display of colors. Thanks for lookin'!

 

mystic topaz?

 

Mystic/peacock topaz. As shamster said.

 

Mystic topaz thirded. It's a clear stone with the fancy coating. They were hot for a while, so you find them.