I'd recommend against painting this mask with spray paint.
Spray paint isn't flexible, and will crack and chip off the flexible latex.
You will need to paint this with a flexible paint. There are many formulas to make these paints, such as rubber cement mixed with oil paints and thinned with naptha, 40/60 latex and acrylic thinned with distilled water or amonia, or PAX (Prosaide and acrylic 50/50) paint.
You'll have to find what is most available and comfortable for you, but I've been painting with Rubber Cement inks for quite a long time. I like Best Test cement thinned with their thinner Bestine, but naptha works well.