We chose which of our extra bedrooms would be the nursery based on it's color. It was already painted yellow--the other room is white. Right now, there are some classic prints in that room--they are of hot air balloons in various colors. While they may not go with my intended orange/yellow/green color theme, unless they clash horribly with everything, I don't plan on removing them. So while I plan on changing the furniture in that room, the walls and "decor" will, for now, stay the same. But I don't plan on having a theme either, and frankly the colors are just because they are neutral and are both DH and my favorites. So again, playing into what the adults like/want and my laziness.
Definitely agree with those who said it is done mostly for the adults. I definitely didn't want to put a lot of money and effort into something he may not even like later.