How to color mix/overlay an image with a transparent background on another?

I have a model with a color image texture. I’m painting some stains and splatters on it with texture paint applied to a separate image, transparent when generated. How can I combine them? Color Mix doesn’t seem to handle alphas. (According to my Googling, in 2013 there was an option where it would.) Other blending modes don’t work–multiply taints colors, lighten means the splatter has to be darker to show up (same problem with darker), &c.

Mix looks OK to me. Are you forgetting the Texture Alpha to the Mix Factor connection?

Hadn’t forgotten it–didn’t know that was the trick. That was exactly what I was looking for, thanks!