Welcome to the forums! White is the hardest color to paint and airbrush. You have to make sure that your paint is mixed up pretty well. Are you painting acrylic, laqour, or enamial white? I use exclusively acrylics and my advice is that you shouldn't dilute white paint down when you brush. Some modelers like to dilute paints when they handbrush them, which is ok, but for white, don't dilute it unless it's thick and starts to get gooey. It will take a couple coats, but it's worth it. If you can't get white to show good, then there's a paint I use to simulate white, but it's actually a light grey and brushes on way better that white. It's Model Master Acrylic camoflauge grey. It's almost white, but doesn't act like white paint when painting it, but when it's dry it looks like white. I'll try to get a picture up of what this grey looks like when dry.
As for the tracks, I would paint them black and let them dry one day, then drybrush them burt iron or alluminum. Hope it helps!