if it still doesnt work for u turn off texture in the brush options, cause if u made the brush or using a made brush from someone else it will most likely have textures for better effects. this means parts of it will have lower opacity and by turning it off nothing will show through it. Hope this helped ;)
How are you finding your brush opacity? I've reset everything to no avail. I see my layer opacity at 100, but cannot even get to brush opacity. My hardness is 100, my spacing is 9. The best clue I have is that when it is in color mode, I'm getting these translucent colors, but when I switch to luminosity, it gets as dark as I want but neglects the color variances across the original object being painted a different color.
I have a similar opacity problem with the fill area tool not being completely opake, say when I define an area in a layer over a photo, color pick from that area on the photo so it gets an average color, and then trying to fill a shape, it is not a solid color but certain values from the photo show through. suggestions?