A number of issues arise with these helmets. The first to immediately jump out is the use of two base colors. The current helm, of course, uses a single base color. This makes it very simple to apply dye to the helm. But there are many two color items already in the game.
Swords are one example, with the blade and haft being the two separate colors.
Only the blade is dyable of course, the haft being a constant gold color. There are several options and, not being a Realm programmer, I cannot presume to know which is the most feasible. This option would work much like clothing did in the old days. If you wanted a green tunic, you bought a green a tunic. Buy a helm and dye it, then dye your backpack to change the secondary color.