Greyed out can also be spelled greyed-out, grayed out, or grayed-out. Grey is the more common spelling in British English, while gray is the more common spelling in American English.

gray out (third-person singular simple present grays out, present participle graying out, simple past and past participle grayed out) (computing, of a UI element) To make (a visual element) gray or lighter in color to indicate that it is disabled or unavailable.