Well I'm glad you asked..
Not my initial idea, but the person is too lazy to post anything. I thought it was a great idea though.
Seeing as it seems that everyone's arsenals are cluttered with unused common materials, it would make sense to be able to use them (a tonne of them) to craft accessories. A small crafting fee perhaps to create each.
As for the different colours (e.g Military / Fancy), perhaps a colour dye? (similar to that of the personal colours). For special colours (Prismatic / Volcanic / Divine), perhaps maybe they require 5 of the regular coloured accessory & an uncommon material to craft them?
Clearly this is just a really unorganised post that isn't really written well at all. It was just a bunch of ideas thrown in. (Quantities of materials / accesssories / crafting fees not entirely thought out)
On a side note, prismatic weapons / shields would be lovely too. If armor can have parts of your own colour, why cant they? ;)
Thanks for taking the time to read this awfully scrappy post!
Getting a random accessory requires both an iron lockbox (which is relatively cheap) but a whopping 750 energy. The costs to craft such an accessory would simply have to be astronomical. Furthermore, it might be problematic for the AH as now there is a price ceiling.
Primatic weapons might work.