A bit of clarification - the dark edges to a watercolour wash are extremely thin - perhaps thinner than your ink line.

This is a good example. Notice how the paint is affected by the grain of the paper, and the way it bleeds into the grain at the dry edge at the bottom of the swatch. The bottom edge is also a classic example of the line of darker pigment I was referring to. Unless the paper is damp when the paint is applied this always happens with watercolour.

Watercolour wash.jpg

It really is just like a controlled coffee stain. A pretty blue one in this case