I’ve been delving into 2.8 grease pencil a bunch and noticed this artifact (see gif) when drawing with low strength (opacity).
I suspect there is no real way around this due to the nature of how grease pencil works.
When you overlap a stroke onto itself (without releasing) it “multiplies”(?) the the overlap in blender.
Ideally it would only do that when you overlap previous strokes. (like it does in photoshop)
I could not find any post here or bug for that so I thought I would share and hopefully hear your thoughts and opinions.
We know this problem and we are looking for a solution, but it’s not easy due technical limitations. The problem is the thickness is greater than the distance between generated points.
About the color, be sure you have alpha = 1 and the strength of the brush is 100%. Test using the strength brush over the stroke in sculpt mode to get full opaque the line.
And about photoshop, the difference is they use a bitmap representation, and we have a geometry information to calculate the stroke. They are totally different worlds.