A good match that I use is a combination of Valspar 5007-2B lead cast (Found at Lowes) or you could substitute this with
Home Accents "London Grey". Next I use Home Accents "Nutmeg" and finally Rustoleum "Dark Taupe". Basically what I do is
do a quick pass of the gray over the entire track then a quick pass of the Dark Taupe and the Nutmeg to hit the rails.
Letting the mist of the browns hit the ties also (Makes a good Greyish brown look to the ties). Then If I want a new tie look
I brush paint some Black on the ties.