Assuming you're talking about airport outlines (rather than the centrelines), are you using the SBS high-res ones, or the ones that come with the RadarBox software?
Must admit that, either way, I can't think why just those should be different colours.
EDIT - from your other post, it may be that you're not zooming in very close. If you are using the SBS outlines, they are crammed with taxiway markings, so from a distance they seem to be a different colout. That may be the problem.
Rod