Buy some oranges and some red or some orange/red little bottles of Testor's or similar at a hobby or craft store (I get mine at Michaels), and a little pack of cheap fine tip art brushes. Try a couple of different mixes to get something that's close enough. Use the 6 foot/2 meter rule - if it's not visible at 6 feet (better yet, 3 meters/9 feet), it's irrelevant. You will not notice it once you get over it, and anyone else will never notice it.
Even if you dabbed pure red on that little nick, it would be unnoticeable at anything more than up close.
But the best thing to do is get a chain stay protector in a color you like - black probably and just cover the entire chain stay because you'll get more nicks there. IF you're not familiar, just do a web search for options. Most are just very tough stick on tape type stuff. All my bikes have them, some clear, some black.
FWIW, I challenge anyone who has owned and ridden a bike for any meaningful amount of time and mileage not to have blemishes like this. It's not even a scar, it's a blemish.
Last edited by Camilo; 12-01-22 at 08:11 PM.