Dunno if this works for everybody, but I've noticed that I seem to get more dye drops in post-searing regent valley. Usually, by about the 4th set of encounters (Bandit or Charr), one of the dead enemies will have dropped a dye.
One of my guild members (Elric, who has posted a great farming guide here) favours this area too, but another one of my clan seems to have a lot of luck around Sardelac sanatarium. I think it's possible that the further you go in the game, the amount of Dye drops get scarcer. I didn't get a single dye drop in the Wilds, and spent a lot of time there!!
Has anyone else got a particular Dye drop hotspot that they want to share, or is it just amazing coincidence?
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of post-searing ascalon area and get into the Shiverpeaks, dye isn't that big of a deal anymore. The prices are fairly reasonable now as well.