It would be very cool to have some way to add the "dye stamp only" colors as an actual outfit store usable single dye color. Given they are already in the game in a way it does not seem like it would be hard for them to be implemented.

Perhaps they could sell a crown store house item dye station that allows a player to take a dye stamp and deconstruct it and choose to obtain one of the 3 colors use in that stamp? This would suddenly encourage a lot of people to purchase crown to buy the house item used to do this AND buy dye stamps with new colors they do not have. There are a lot of people that would probably end up spending quite a lot to make all of the colors available.