The current problem is while you can buy a limited selection of dyes in the Vistani Camp near the Outskirts, in Degannwy and from some of the Vallaki city merchants, a lot of those dyes have inconsistent names when compared to the existing lists that we have on both the forums and on the more frequently visited vendors, so you're forced to play a roundabout guessing game on which dye is actually the colour you want. Considering that Vallaki and it's surroundings are the starting area for new characters, this unfortunately means you might spend much more gold just to find a single dye.
Ontop of that, there's no preview dummies available. Yes; you can take a trip downriver to Krezk or go all the way to Port but that is horribly inconvenient for what is essentially a non-mechanical aspect of the game. At the very least having the dyes renamed to their proper forms would be helpful; having tailoring dummies to test clothing designs would be even better, though a lot of people argue that Vallaki's lack of these dummies represents it's financial state when compared to more affluent locations.