I could be wrong but I thought Riv was infamous for
not having paint codes or touch up paint.
And I remember reading somewhere that Grant had tried to revive the old orange of the XO-1 but was not successful. I also seem to remember that he said it was the best orange he'd ever seen.
I'd wager that the orange of early Hillbornes and the current orange on Appaloosas & Roadinis is an attempt to have something close on Rivendell frames.
A paint that's close to the Clem (and Appaloosa) mustard is Devin's glorious Rat Trap Pass frame (
as seen on iBob here). It's painted in RAL 1027, "curry."
Best of luck with your project.