What you suggest is nearly correct.

The contrived "matrix" on magnesite imitations is typically brown—as it is for quite a few varieties of actual turquoise, and particularly a lot of (but not all) Hubei Chinese turquoise. The "matrix" effect on magnesite is not "a strange brown." It is a typical brown for the material it imitates.

Whereas, as I mention, the natural matrix lines of howlite are wispy and gray—and usually look very different from both real turquoises and magnesite imitations.