How to stop a brush from darkening the color of a previous stroke?
In the image above, I showcase the problem.
I have some marker brushes that have a nice texture on them which shows the tooth of the paper. I'd like to get a more consistent look when I'm coloring in an area, but when I go over the same area in more than one stroke, the paint darkens (Example #1). In example #2 I went over the same area, but within the same stroke. The color stays consistent in that case. This is the effect I want, but with multiple strokes. In example #3 I tried fixing the problem by selecting the area around the initial stroke with the magic wand and painting it in, but that leaves a white outline over the original stroke. Expanding the selection by 1 pixel results in a dark line between the strokes.
So is there a way to solve this problem so that I get a smooth, consistent look with multiple strokes, like in example #2 Where I only use 1 stroke?
You're using a Brush that has transparency built into it. There's no way around that effect as a result without opening the .abr file and adjusting the opacity of the stroke which would defeat the purpose of using that brush to begin with.
For example here is a Watercolor Brush on white background:
If I remove the white background even though the brush flow and opacity is 100% you can see it contains different levels of transparency within the actual brush:
Your best bet is what you did in number two combined with masks to control the form.