Preventing adding up of colors for multiple brush strokes

This is somewhat a newbie question, but I couldn't find any solution. While painting, if I lift up the brush and start painting again, colors start adding up at intersections. This makes it hard to make it look smooth. As you see in the image it is darker in the place where two brush strokes intersect.

The behavior I want is, as if brush is not lifted, painting over the same area will not change the color unless it is darker (Max filter maybe?). Or maybe I should change the way I work. What do you suggest?