As an example, you could take a circus nursery and use vintage posters and old fashioned toys and furniture rather than the bright, shiny stuff that you would use if you wanted a modern room for your baby. By using that process, practically any gender neutral nursery theme could be dressed up with old fashioned fabrics, artwork and furniture.
When I saw this pictures of an alphabet theme vintage nursery for twin boys and girls I felt that it was a perfect example of what I'm talking about.
Rating
Vintage Nursery for a Twin Boy and Girl by: Anonymous
The picture of the vintage nursery for a twin boy and girl has WAY more baby blue in the color scheme than it does pink. Maybe it's just my computer monitor, but I had to look very close at the picture to find any indication that a baby girl was considered in the decor.
Maybe it's because the chipped antique white paint had so many blue undertones that the blue became so dominant but I believe that a slightly stronger shade of pink (again if my monitor is accurate) might have been pretty.