Boy/Girl Nursery

I just found out I am expecting a little girl this sunmer. I already have a one year old son so once the new baby is old enough to be in her own room they will be sharing. My son has a baseball themed nursery right now with navy and gold walls, with white furniture and black accents. Any ideas as to how I can make this room gender neutral with doing the smallest amount of painting/redecorating possible? What are some good gender neutral themes? I know girls can like baseball too but I want to make the room THEIRS instead of keeping it all HIS.