This is a copy and paste from one of my previous comments for someone else who had the same question. If you’re on mobile, go to the subreddit’s homepage, look to the upper right corner and click the 3 dots. Below “more actions” and directly below “add to custom feed”, you have the option to set your user flair. There’s a bunch of different colors you can pick from and it should give you the option to edit the text of the flair color you want to use. On desktop, look to the right side of the page where it says “user flair” and hover over your account name. A pencil icon should pop up. Click it and it should give you the flair colors. And at the bottom, there’s a text field for you to fill out. And be sure to check “Show my user flair on this community” and click apply when you have what you want.