As with most of the axes above, and with most PRS's, they use a stain or dye as a wipe and then sand most of it off. This darkens and intensifies the grain, depending on the color of the stain used and how much is sanded-off/left-on.
While Alembic does do burst and tinted finishes (besides opaque painting), I don't know if they do staining of grain.
Mica, Val, Dave?