Minecraft/Dye

Dye
Stackable	64

Dye can be used to change the colour of leather armour, wool, beds and sheep.

Obtaining

Red: Made from poppys, rose bushes and red tulips.
Blue: Made from lapis luzali and blue orchid.
Light blue: Made by combining blue dye and white dye.
Green: Made by smelting cacti in a furnace.
Yellow: Made from dandelions and yellow tulips.
Orange: Made from orange tulips and combining yellow dye and red dye.
Brown: Made from coa coa beans.
Magenta: Made by combining red dye and blue dye.
Pink: Made from pink tulips and peony.
White: Made from bonemeal.
Light gray: Made from lilly of the vallies, cornflowers and white tulips, among other things.
Gray: Made from black dye and light gray dye.
Dark gray: Made from black dye and gray dye.
Black: Made with ink sacs.

On Bedrock edition, you can only dye leather armour by dyeing water in a cauldron, then pressing "use" while looking at the cauldron and holding the piece of leather armour you want to dye in your hand.
Dyeing is much easier on Java edition. There, you just combine the armour in a crafting grid.