I use a product called Tumbler. You can pick it up at a few different automotive refinishing shops.(it is actually for stripping wax and debris from paint) You just wipe on and wipe off, no scrubbing, have been using it for a little over a year and there is no difference is discoloration of the belly pan, seat, handlebar pad cover, or anything else. It is the best product I have found yet.
its a very good parts cleaner too(kinda expensive to wash parts with though)