Medium gray real stone paint in the case of dry mask! Then it was rained heavily! All milk white! Does it turn gray after work? What's going on?

I don't know what kind of varnish you choose, but in your case, the surface layer is permeable and uneven in drying. If you choose a low-grade water-based finishing agent and add too much water and uneven roller coating, what you said will happen. In addition, it depends on what kind of sand you use in your real stone paint. If it is a real stone paint mixed with gray colored sand, this will not happen. It is estimated that you use quartz powder and color paste to adjust the color. If it is like that, it is normal for it to change color after a period of time. It is recommended that you use colored sand stone paint and use a good water-based finishing agent (add some water and coat it evenly). In fact, if you have the conditions, you should do it well or use an oily finishing agent. I hope my answer is helpful to you.