There is a technique that is far superior to pre-flashing color RA-4 paper.
Go here: http://www.davidkachel.com/history.html
Then read the article: Zone System Contraction Part III — SLIMT's
Color is not mentioned in that particular article; I've just been too lazy to add the information which was published in another article at the same time. This technique works on RA-4 color paper exactly as it is described for B&W, except of course, final concentration will no doubt be different. Results can be controlled from very subtle to very extreme. Your option.
Another author invented an increased contrast technique for RA-4 paper at almost exactly the same time. Together, we invented variable contrast color paper. Unfortunately, the world stopped caring at about the same time. Digital had raised its ugly head.
Oh, both techniques require a small change in filter pack. But then, so does everything else!