Topaz Colors - Red?

Two yrs ago I bought some red topaz at the Tucson gem show. The
dealer said red topaz is really white topaz that has been treated (I
think diffusion was the word he used). The color is only on the
surface of the stone (unlike blue topaz) and if you chip the stone,
you will see the original white topaz. Some of my red topaz is
reddish/pink, some is pink. I tell my customers that it is treated
stone and they don’t care because they’re buying it for the color.