After reading the latest Dev Q&A on weapons and armor, I was rather disappointed at their comments on the barbershop and visual customization. Personally, I would love more customization, even if it's just more hair colors and hair styles available in the barbershop. I was trying to think about how I would add this, and here's what I've come up with.
I wanted to include as many professions as possible, and allow players to create new looks or copy existing NPCs. I also wanted to give people a reason to go run old content and have players talk about what they're wearing.
Engineers would make a camera-like device. Using it would allow a player to take pictures of any npc. Then you would take the picture and find a tailor, leatherworker, or blacksmith (depending on whether you were wearing cloth, leather/mail, or plate). Give them the picture and they'd be able to change your armor to match it. Now, if you want to look like you're wearing a particular piece of armor, you need to go get that piece if you can't find an npc wearing it. Basically you need something for the crafter to work from, which is pretty reasonable. Photos could even be sold on the AH, so if you manage to get a shot of a rare npc, you could get some gold.
Now, this could cause some PVP problems, but the system could simply be set so that your armor reverts to its original appearance in arenas and bgs. Plus, inspecting you would show the original armor.
I'd also love to see the addition of dyes, made from milled pigments by alchemists.
And yes, this is because I totally want to wander around in a green and silver version of the blood elf guards armor. Plus, my paladin could run around in a dress, and my mage could look like she's wearing plate.