I use yellow and brown wires for feeding my track. Red and Blue colored wires are for all my AC accessories like street lights and interior lights.
In the above picture you'll see all the essential tools needed for wiring, colored wires, a wire stripper, solder and a soldering iron.
I solder feeder wires to every rail joiner, because these are the weakest points in every trackwork. They might sit very tight at first, but changes in temperature make the rails shrink or enlarge and after a while there´s grime or occidation building up between the rails and the joiners. This causes the trains to stall. because there´s not enough current passing from one track to the other.
I make sure that my feeder wires are long enough so that they reach to the fascia. Then I twist a couple of them together and slip a piece of shrink tube over the wires.
Then I twist a piece of 2.5 mm gauge wire to this and solder the twisted wires together. This is the same wire gauge that I use for my bus wire around the layout.
I connect the "bundled" wires to my bus line with 3M scotchlock suitcase connectors.
The suitcase connectors are very handy, because I don't have to strip the bus line all around the layout to connect my feeder wires. All my wiring is located behind the fascia board for easy access