Why won't my black brush stay black

Okay so the problems comes with a smoke brush I made for a project, I changed the color to black smoke and it works...until I put it on a gray background. When I put it on a gray background the smoke turns white and the stroke color is black and the smoke is black whenever it isn't on the gray background. I can't figure out how to make it stay black. I've changed the colorization method from tints and shades to none, hue, or just tints nothing works that way. I've changed the document color settings that didn't work. I have looked up vidoe after video and nothing works.