This question isn´t particulary lame, as most Amiga-software does not include an uninstall-thingie.
I don´t remember about MagicWB, but my guess is that it adds something to s:user-startup (or else s:startup-sequence) read both files. most probably it added a comment line above the call to some binary. Reverting to the original colors & icons may take some extra work.
Maybe you should wait for an answer from another MagicWB-User ... he might know some tricks.
