Fairly easily. The blue and green ones I do not have an issue with, but the red one is close enough to the brown background that it's practically invisible to me.
Normally that's helpful, yes. But it doesn't always work. This particular quest for example ends up showing half of the Churning Mists on the map when I do that, I spent a good 3 minutes trying to find it even using the hint the game gave me.
Yeah, having an ant-trail type effect around the border would work really well, although it would be annoying for regular users I suspect.