White, blue, and red are great gender-neutral colors to decorate a nursery with if you don't know the sex of your baby. Simply add more masculine or feminine touches once your bundle of joy arrives. If you're going for a more modern look, choose furniture with clean lines. If rustic is more your thing, choose furnishings with warm wood tones.
If you love lots of color, don't be afraid to run with it. Choose an item that will live in the room, like a blanket, to draw inspiration for your color scheme. Work the colors throughout the room so it flows and looks cohesive. As you can see with this nursery, they incorporated the pink, green, blue, yellow, and orange from the blanket into the pom-pom garland and tapestry. The nursery has more of a feminine vibe because of the pale pink rug and peach-patterned bin. This can be easily remedied by highlighting another color from the blanket.
When I was pregnant I knew I wanted the nursery to be a calming blue color, whether the baby was a boy or girl. After finding out I was pregnant with a boy, I decided to go with yellow, green, navy, and gray. It was an interesting choice of colors, but I made it work by incorporating colorful artwork -- which are actually old American Geographical Society programs and books on book ledges -- to bring all the colors in the room together. I chose a white crib, dresser, and garden stool to allow the colors to pop.
Don't be afraid to go bold. This bright yellow-and-pink nursery packs a lot of punch. The color blocking on the walls and window treatments gives the room a modern feel. Remember to use the darker color on the bottom portion to anchor the room. Light colored furniture, flooring, and accents allow the bold walls and curtains to shine. If you do decide to go with bold, saturated colors, make sure the room gets enough natural light so it doesn't look too much like a dungeon.