While Jin has multiple choices of armour to wear throughout the game, he's also able to customise the colour using dye. Here's how.
Ghost of Tsushima: How To Dye Jin's Armour
To change the colours of Jin's armour, you'll need to purchase dyes from merchants around the Isle of Tsushima. Each dye will set you back 10 flowers, so you'll want to be constantly on the lookout for them.
Flowers have white petals and green stems, and you'll often find them while going about your business.