Neat idea. The ability to store all your dye in your transmog closet, and when you select a piece of gear to transmog, it also opens a pallete down below, with all your available dyes. Clicking on a dye shows you a preview of what it would look like, just like the transmogs. Clicking confirm saves it and uses up one of the dyes.
Would need better lighting in the closet as well.
Side idea. Very very rare permanent dye drops. All dyes have a permanent drop added but are far rarer. Like jet black would be a 0.001% chance. Or something. Putting these dyes in your closet would allow you to dye whatever gear you want any amount of times.
Just some thoughts.