mask with 24-bit color screen

[butsch@ge-dab.ge.com]

I have been trying to get the ":mask" option to work with drawing
on our 24-bit color screen, and have not been having any luck.
Does anyone have any suggestions on where to find information
that might be of help?

I hace been trying to get this example from the manuals to work
with color so I can work out the details.

                (graphics:with-room-for-graphics (t 200)
                  (multiple-value-bind (bitmap x y)
                        (graphics:with-output-to-bitmap ()
                          (graphics:draw-triangle 100 50 200 150 300 50))
                    (graphics:draw-rectangle 0 200 400 0
                                             :gray-level .33
                                             :mask bitmap :mask-x x :mask-y (+ 
100 y))))

Thanks in advance.

Mark Butsch