Basically, it's an exploit that allows you to dye your clothes for free. I haven' really explored is much, but it's worked for me the way below:
1) Go to someone who can dye your clothes.
2) Select an item of clothing to dye.
3) Choose a colour. So far I've dyed both parts the same colour (right and left click on a colour)
4) Tick the check box beside "Apply color(sic) scheme to all items"
5) press the ESC key
You'll exit out of the dye menu and your clothes are pimped out!
It work, until you re-equipe equipement or change zone.
Its a visual effect and nobody else then you see it.
Its a copypasta btw :/
And yes, its client side
Doesn't actually work as in "Dyeing" your gear. This works as intended as far as I know, and this is just the visual reference that only YOU see when Dyeing.