So, here's what I'm thinking: Special dyes (or effects that can be applied over existing dyes) to ramp up the cool factor on our armor and weapons. One could be some kind of stardust effect, like you're looking in through a window to a starry sky that's inside your armor.
They could be obtained through a wide range of tasks like Veteran Trials, Master Writs, Holiday Events, or even through Achievements, but once obtained they'd be account-wide like the original dyes themselves.
Guildmaster of Spectral Liberty - Xbox One - European Megaserver