Modeling in Nscale change many rules which are used in bigger scale.
However I use a simple method which has give me excellent result.
I airbrush the track whith a earth/ tie brown color, in fact a mix of two Golden acrilycs artist airbrush colors.
When the paint is dry (a few minutes) I come back whit a brush and a whole asortiment of brown Vallejo colors, from deep brown to light brown .
Here an there, randomly I retouch by brush some ties whith the different brow colors, I also use some dark gray.
This touch up break down the uniformity of the color of all the ties.
When done, each file of track is painted whith Floquil, now Testors tie brow, whith a small brush; it seems difficult to do in Nscale but the process is fairly simple , and the result give a real old rusted and dusted rail.
The track is ballasted......slowly in perfect shape whith a brush ( a good rythme is one meter per hour).
I use the Gody Grino method to glue the ballast, I soak it whith Isopropilics alcool diluted whith some water, Its evaporated more slowly trhan pure alcool.
The ballast is glued whith white glue but I soaked whith glue only the exterior of the track, never between the file of rail, capilarity do the job and brings enough glue (in Nscale) to firmly glue the ballast between the rail.
Two days after, I inspect the track, to see there is no grain of ballast glued on the side of inner side of the track, I use a bright boy abrasive gum to clean the top of the rails and the whole area is vaccumed.
The last thing I do is wheather the the track whith a wash of india ink and isopropyl alcool. I also put some rust wash (from Vallejo) on the exterior of the track to simulate some rust on the ballast.
It seems to be a lot of work but I do it on long run of track, two of three days working and whith method I am able to ballast and finish big piece of mainline track in a few hours.