x-display-planes

x-display-planes is a built-in function in `C source code'.

(x-display-planes &optional TERMINAL)

Return the number of bitplanes of the X display TERMINAL.
The optional argument TERMINAL specifies which display to ask about.
TERMINAL should be a terminal object, a frame or a display name (a string).
If omitted or nil, that stands for the selected frame's display.