how responsible is tenant for unapproved paint?

[Benson L.]

I had a tenant stay for 6 years. They were great, but when they moved out, I noticed that they had tried to fix blemishes on the walls by painting it themselves. It was well-intentioned, but this does not work (see picture). How responsible are they for paying to repaint this stuff? They pointed me to this website and HUD documentation that says paint only lasts 5 years. Since they stayed for more than that, the prior website claims I can get 0 back. The tenants feel that I can't really ask them to re-paint everything, though they are agreeing to pay some. Do I have any ground to stand on?