Is brown or yellow mucus discharge ever normal in first trimester....And what if it comes and goes away completely

Yellow yes. Normal colors for mucous are yellow, clear, white, grey, and green. All dependent on hydration and types of food eaten. Brown would make me think of old blood. Possibly from the cervix from intercourse or maybe placenta implantation. If it has gone away and there are no other symptoms, i would just watch and wait. It it continues and is associated with other symptoms, then fu with your ob.