mixing black and white to make gray? I loved my mac nail polish from hello kitty collection "on the prowl", however i finished it. so, i decided that i wanted to paint my nails now. It is 3 am so i cant go to a store ^^ Is it a bad idea to mix the colors together. I have a white from sally hansen salon nail polish line and the random black color. So i only have a little left in the white bottle. Is it a bad idea to mix black into the white polish?