Dye Armor at the Wardrobe
Diablo 4 allows players to dye items in the Wardrobe feature, which can be accessed in each Regional Capital (e.g., Kyovashad). Dyeing is free, and all colors are pre-supplied (i.e., no unlocking).

Which items can be dyed?
All 5 Armor slots can be dyed. Each Armor piece can be a different color or all the same color. If the player wants all Armor colors to be the same, a time-saver is to click and hold the dye choice for a few seconds.
Available color pigment sets
The Wardrobe provides players with 8 dye options. Dyes, or "pigments," as they're called in the Wardrobe's UI, each come in a set of 4 colors. Each color in the set is applied to a different type of material in an item (e.g., fabric, leather, or metal).

Dye reacts differently to materials
Blizzard says that each Armor piece has metadata specifying its material types [1] and that the material types react differently to color pigments (e.g., sheen and vibrancy).
"We added data to the armor that identifies specific materials and tells the dye system what color goes on what material, such as fabric, leather, metal, and other surfaces."

Sources
Article | Source | Date | |
---|---|---|---|
1. | Diablo IV Quarterly Update 2021 Q2 | Blizzard |
Changelog
Ver | Change | Date | |
---|---|---|---|
1.0.3 | Refreshed guide with Release Armor dye information | ||
Beta | Refreshed guide with Open Beta dye information | ||
Alpha | Added higher resolution images to multiple sections | ||
Alpha | Added section on Wardrobe System | ||
Alpha | Published original |