OK, here's the code that works. Set the colorwell class in IB to AlphaColorWell:**
@implementation AlphaColorWell
- (void)activate:(BOOL)exclusive
{
[[NSColorPanel sharedColorPanel] setShowsAlpha:YES];
[super activate:exclusive];
}
- (void)deactivate
{
[super deactivate];
[[NSColorPanel sharedColorPanel] setShowsAlpha:NO];
}
@end