”Paint” a tint on a texture/sprite

What would be the best way to paint a tint on a sprite?

I have made a script that use getpixels and setpixels to be able to paint on a sprite.
I blend the original texture with the ”brush color” and then save to the texture with setpixels.

But now i want to be able to paint a tint on a object. So no matter how much you draw the texture will not be completely overwritten.

I want the end result, if you paint the whole sprite, too look the same as if you changed the color of the sprite. But i want to be able to change one area at a time ”drawing”.

I appreciate any suggestions!