To access these options, select Edit > Edit Stencil. (If you have no stencil selected for editing in the Stencils tray, the Create New Stencil window opens instead.)
As long as this window displays, Mudbox is in stencil editing mode, and any painting or sculpting is applied to the stencil.
Monochrome (black and white, with darker areas more transparent)
Transparent color
Opaque color