Mike,
I'm just guessing, but it seems that you might be able to change the
colors in the knob image structure *after* Intuition has initialized it,
i.e. after you've added the gadget by opening a window or with
AddGadget(). It's hard to be sure about this, however. It's not too
hard to do your own knobs, but I admit that AUTOKNOBS can be pretty
handy.
brent