I've seen some really pretty gender neutral nurseries in a wide variety of colors.
After searching on Pinterest for gender neutral nursery ideas I concluded that pretty much any color can be if you use the right accent colors and/or other decor items. Like blue could totally be a boy nursery color but if you pair it with some white lacy things and maybe some flowers and such it starts to look pretty girly.
Here is a pretty green nursery that I personally think is pretty gender neutral. Still I would go grey, or a pastel-ish mint color.
Or, if you go with beige, get a bunch of cool wall stickers, you can get some that go all the way around the room to add color without breaking the gender neutral colouring. I had a friend do a jungle theme, she knew she was having a boy but wanted the nursery to be reusable.
Another friend did a rainbow theme with pastel colors which worked out great as well, and her walls were just beige.
Someone else mentioned turquoise and that's always a good choice because it's a pretty, non-boring color that can go either way.
Some people opt for nurseries that have a lot of color like like rainbow dots or whatever.
Honestly I think whatever you do would be fine as long as it's something you like. Don't pick a color you hate or you'll probably end up unhappy with the room.
And if you have a color you really love don't worry too much about if everything is matchy matchy or how it goes with the rest of the house or whatever. Plus in the end baby doesn't care what color the nursery is. It's really more for you.
By the time baby is old enough to care you can always change things up and repaint.