Very often I see layouts with very dark grey or even black roads. Take a look outside - are the roads you see actually black? Even in the rain? My tip is to use a medium grey tone as a basis and darken it to suit the season or what you want to depict.
For example, my layout depicts high summer so the roads are dry and very pale. If you are looking for more of a darker 'industrial north' feel to your layout, make the roads a shade or two darker. Use water based craft acrylics (not expensive Revell or Humbrol) directly onto the board if it's a good, sound surface like plywood but if it's compressed 'chipboard', give it a coat of water based matt varnish first. It will stop the paint soaking in and fill some of the small gaps.
Finish off the roads by dry-brushing very dark grey tyre marks on bends and against kerbs. It adds texture and looks like they've been used.
I guess I'm saying that just because TrackMats depict roads as very dark grey, doesn't mean that they actually are.
And the same goes for grass - it's NOT bright green.. it's sort of several shades of greenish stuff with brown bits!
I hope this is of some use. Get back to me if you need any further detail.

