Bek, I'm wishing we'd gone for green too now! Easy to add either blue or pink to it after bub is born and it would still look nice. Bah!

Wonder if I could mix the yellow with a blue to get green hmmm...could always try a small sample and see what happens!
Talk to the people at the paint shop. Most paints start with a base and then they add tints to get it to the colour you want. I have taken paint back and got them to add tint to change the colour. It is a bit more creative than just following the recipe from the start, but you can get pretty close to a new colour you decide on.