since no one has responded....
There are some colors that were not exported from japan, I've heard......possibly some to euro countries but not the U.S.
No documents I know of to prove one way or the other except maybe Honda brochures or magazine articles reporting as such. Another possibility is looking at a parts book as honda did put a color designation at the end of tank and side covers. For example, 1975 U.S. 550F's colors were "rc" and "pb" , which is "sunrise metalflake orange" and "sapphire blue".
Honda used "candy ruby red" on early 750's......
subsequent years show other "reds"
the lubritech paint schedule doesn't show a red for 500's...
