I know my comment is late, but this feature would be so exciting! There are certain outfits I really like the shape of - but not the colour - so tweaking them would open a lot of clothes to mix and match with. This could make unpopular outfits desirable and even get people to buy multiple copies of an item so they can easily switch the colour. Players will also be able to twin the same style but stand out with a new colour.
However, this would best work on outfits that come in a single colour by itself, with white, or with black.
There is the worry that the hue slider won't meet expectations since the brightness, saturation, contrast, and warmth/coolness can't be changed, as well as individual parts of an outfit. I don't know if such adjustments are even possible... For e.g. you can't change a pastel green outfit into a rich olive green. Changing the hue has a chance to severely reduce the quality of an outfit and there can also be problems with blending the cell-shading with the main colour. E.g. I would prefer blue shading on my outfit compared to a purple aura.
The ideal would be if Nexon allowed players to edit/recolour outfits themselves (possibly even frame-by-frame). This does sound like a lot of work, but there are people who would be willing to put in the time to get their outfits perfect. Then again, who knows how the game will break from such an addition? And if you implement the dye system from TMS but later decide to improve it, what do you do with those who already used it?
Nevertheless, I really want this feature.
P.S. I'm jealous of all the CMS player designs making it into the game.