Just a heads up: in the release version of Leopard (9A581), there seems to be a bug with the NSColorWell control. Specifically, if its focus-ring type is set to “none”, it won’t visually update itself until its window loses focus. It still functions normally code-wise, but it won’t update its actual appearance.
You can reproduce this yourself in Interface Builder. Make a new nib with a window, and add an NSColorWell. Use the Inspector to set its Focus Ring type to “None”, then test the interface (command-R). Click on the colorwell and you’ll see the Color Panel, but the colorwell won’t look selected, and nor will it update its swatch as you choose colors (though it will always report the correct color to your code).
Reported as issue #5579783.