The thought occurred to me the other day that one could easy make a Christmas iMac G3. You'd simply need one Strawberry iMac and one Lime iMac. Take them apart, then swap out the colored panels to make a mixed red and green system.
Alternately, you can use the later Sage and Ruby iMacs, which feature much richer, more Christmas-like colors. But Sage and Ruby iMacs are not as common as Strawberry and Lime ones, so that might be a problem.
I haven't actually done this myself, but I made a graphical mock-up of a Strawberry/Lime mixture that you can see above. If anybody actually makes one of these Christmas iMacs, please let me know!