I used to shoot the whole track with a color called sweet chocolate that came in a rattle can from K-mart. (In truth, any similar flat brown will do.) It does a pretty good job of simulating creosoted ties and rusty rail, but has to be done before ballasting, so is out of the question for you. Since you're going to be brushing, mix up something of a dull, dark rust color that looks like it's been there a long time. Colors like the rust that Floquil made are too bright, too orange and simulate rust that's too fresh. BTW, the Noch grass mat looks very good.
A very famous model railroader once said, "Every picture tells a story, don't it?" This one more so than most. Looks like someone is coming home for the last time on the express car. Excellent shot.
As you already have scenery around the tracks, I would recommend using the Floquil or Woodland paint pens. https://woodlandscenics.woodlandscenics.com/show/category/TrackPainters
Love the frozen over landscape and the ice in the trees. I bet the crew would welcome a nice fire in the caboose stove.
Candy, leave the rail-head shiny for well-used routes or sidings. Otherwise a lighter rust color than the web and base for tracks that haven't been used for two or more weeks. BTW, there is no "standard" rust color. The color depends on the rail's alloy, and the local environment. For instance, the color will be different for rails near salt water, than for rails inland or in arid areas. Go to areas that are similar to where you are modelling and try to match that color.
OK, next you're gonna tell us you bought a caboose, made it into a home, and are living in it in the back corner of an ex-New Haven yard.
Good points, although anyplace we expect to run an engine is going to have polished railheads. The idea of rails showing a different color of rust by region, composition, etc. is something that had not occurred to me, but makes perfect sense
We had some fun here this weekend, at a Sunday afternoon op session. Here we have the D&RGW 3129 leading 4 other units on a westbound freight. Here is a well known propane and propane accessories dealer. An abandoned farm A couple of CF7's working the Hindsight Industrial RR switcher. And some MofW folks getting ready to replace a frog on Main track #1 Thanks for looking.
If you want to show age, stay away from shades of orange. That color spectrum is only good for fresh corrosion. That would be the top, wheel tread area only. Too many folks use it on wheels and rail web/sides. Real rail will be hues of very flat brown. This is not just aged rust, but the grime of passing trains, weather, etc. Take your camera out to local tracks. Grab views of rails in active main tracks, sidings, spurs, etc. You will easily see what I am describing.
I used an old Floquil color, Red Oxide Primer. It seems a bit to orange, but is ok after I weather it a bit with an india ink/alchohol wash.