capi question from new lispworks user

Does win32 support alpha channels?   For example, the following code 
produces correct results on my mac, but not on the pc.  Am I doing 
something wrong or is it simply not supported in win32?  Thanks for your 
help!

(defun display-circle (self x y w h)
    (gp:draw-circle self  50 50 50 :filled t)
    (gp:with-graphics-state (self :foreground (color:make-rgb 1 0 0 .5))
    (gp:draw-circle self 100 100 100 :filled t)))

(capi:contain (make-instance 'capi:output-pane :display-callback 
'display-circle))