It is certainly possible to artificially color turquoise. Chalky turquoise, for instance is generally soft and porous, and pale in color--and would accept color well.

But here's the thing--when turquoise is soft it is often "improved" by being dipped in melted wax, or by being plasticized. There are lots of ways to "improve" turquoise, and the most-recent techniques (that remain secret) are the most successful.

But just dipping turquoise into wax or plasticizing, both darken or enrich the color. There is usually no need to resort to artificial dyes. When such a bead is broken, it appears more-pale inside, and more-colorful on the surface--like a thin skin.

Nevertheless, if a broken bead displays a different tone of blue than the interior, then it most-likely has been dyed.

Some turquoise has been both dyed and plasticized. In past times, in commercial terms, plasticized turquoise was referred as being "stablized." If it were both dyed and plasticized, it was referred to as being "treated." I suppose this naming approach is not longer standard. But forty years ago it was useful (assuming the seller was not just lying).

Jamey