Return RGB values of the color COLOR on a termcap frame FRAME.
If COLOR is not directly supported by the display, return the RGB
values for a supported color that is its best approximation.
The value is a list of integer RGB values--(RED GREEN BLUE).
These values range from 0 to 65535; white is (65535 65535 65535).
If FRAME is omitted or nil, use the selected frame.