Reply to "What do you use to put in between rails to make it look like the tracks are in concrete?"

This is Krylon Camouflage 4291 Khaki.  There is a difference between aged concrete and concrete.

Note the three layers to the floor. Luan board bottom, masonite, slightly thicker middle and luan board top, cut to fit between the rails and finished/smoothed with drywall compound before paint. 

Profile of the floor detail.