Dye Water can be found in loot boxes, as can the ingredients needed for transmogs. You need a Transmute Potion or Dye Henna to change your skin or hair. Once you have Dye Water, flower colors match the dye color you get. If you’re struggling to find the items you need when opening loot boxes, restarting the game can help - but that’s something I’m fixing in the next bugfix build so restarting won’t be necessary.
You get (random) previews of what an item can brew with so you can add a single item to the brewer a few times to see any possible pairings, but I’m making it show multiple in a future update.
Hope this helps! :)