neutral colours?? We're currently decorating the spare room ready for Jellybeans arrival in October. I also have a 14 year old step-daughter who stays during holidays, so we're doing neutral colours for that baby, and my step-daughter's area of the room (not that its a large room, but around her bed etc) will have her posters and teenage-girl bits & bobs there. At the end of the day, your baby isn't going to care how the room looks - so I'd stick with mutual colours for girl or boy, but put a few of your son's favourite characters around as well. You don't say how old your son is, but i'm sure then when he comes to stay, it's to see you and not the decoration anyway.
Hope it all works out well with the Court battle xx