By getting new armor and using dye, you'll change how Aloy looks in Horizon Forbidden West all the time. Another way to do so is to change face paint, which will also signal a kind of alliance with the many factions in Guerilla's game. If you want to use the options you've unlocked, here's how to change face paint in Horizon Forbidden West.
How to Get Face Paint
Getting the face paint options is nice and simple. You'll get them as rewards for completing various main and side quests in Horizon Forbidden West.
Even before you start some of the quests, you're able to see what the rewards are, including the face paints.
How to Change Face Paint in Horizon Forbidden West
Once you've got some, you need to find a Painter to equip a face paint in Horizon Forbidden West. There aren't many of them, but they're the only people who will do them for you.
You're looking for a strange tool looking icon, like the one in the screenshot below, and the first one you'll come across is in Scalding Spear. There are two more to find later on, but the easiest to go to is the one at Scalding Spear.
If you talk to the person there, you'll be able to choose the face paint you want to use. You can change it as many times as you'd like, but it costs 10 Metal Shards each time.
Since Metal Shards are pretty easy to come by, you won't be worried about spending 10 on a new face paint change. Since there aren't many painters in Horizon Forbidden West, though, you probably won't be changing that often.
Face Paints are also cool to equip when you're taking pictures of Aloy in photo mode, often in front of beautiful vistas.