White glue or matte medium for securing ballast?

[Sumpter250]

As soon as the solution dried all the N scale Atlas code 80 (what I used at the time) appeared to 'tarnish' (almost a 'weathered' look). This was only where I either sprayed or using a eye dropped applied the mixture. I don't want to have the same problem (though the affect is nice) since I'm concerned about it affecting connections between the sections of track (all flex track)

If by that you are stating that connections between sections of track, are accomplished only by the rail joiners ?
Each individual piece of rail, should have a wire soldered to it, and electrical connections should be via the wire, with the rail joiner only there to keep the ends of the rail aligned. Saves you from the eventual headache of " trying to find where the voltage went to ".
As to the "tarnishing" ? I've never had that happen with a 50/50 water/white glue, with several drops of detergent added as a surfactant. Maybe you should have your tap water "tested". :o

A product that " turns only the rail rust color ", while gluing the ballast ?? --- Now there's something I would definitely buy !!