OutlinePass color and antialiazing

Hey, im trying to use the OutlinePass in my project. The scene ive created is mostly white so im trying to get a outline that is black or colored. The problem is that the outline is always somewhat whitish/unsaturated when setting visibleEdgeColor or hiddenEdgeColor. See this demo where the visible color is green and the hiddenColor pink.

How can I make it saturated?

Also is there a way to use SSAA after the outlinePass to get a smoother line?

The problem is that the outline is blended additively over the beauty pass. This kind of blending makes it hard to produce a darkish color. This is in some sense a limitation of the used approach.