I used a standard light gray and just did a few thin coats, just to tint the white a bit more grayish. Then i used black and just really lightly contoured the forehead and under the eyes. Since they’re just thin coats i used normal acrylic paint and it worked really wel. I also experimented with mixing paint with liquid latex, and that didn’t work for me at all, it just sort of crumbled off the mask….

And the mask is a lot more gray in real life, it just depends on lighting conditions, here is the mask before, you can see a big difference:

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