Yellow and Pink is a classic color scheme for a girls room. Maybe a bright blue and green for a boy. Lime green and hot pink are complementary colors that would also go well together, if the kid likes bright and loud colors. Other examples of complementary colors are purple and yellow, green and red, orange and blue. It just depends on tastes and personality.
If the colors are very loud then the room can look smaller, but if the room is decorated in very soft, pastel colors then it can look like an adult's bedroom.
If your child likes something that stands out I would say to go with the neon colors I know my daughter LOVES her room and it is very bright and fun. But she is a teenager and the younger ones would probably want something more settle like if it was a girl probably a light pink or a purple. Or a boy probably a sky blue or a shade of green
Depending on the age of your child or children why not let them have a say in the choice of the colour of their room?
Boys tend to like the deeper colours such as reds and blues and greens. A lot of boys like colours which reflect their hobbies and as a lot of boys like sport they often want the colours of their teams on their walls. Football, ruby and other 'sports' colourers seem really popular with boys.
Girls too reflect their interests through colour schemes. Again this depends on age. Younger girls are very into pink and related colours at the moment. Pinks and beige go well. Matching doesn't seem to matter much!
Do ask them what they really like and unless it's something really horrible let them have some say in the choice.
Contrasting colors look great in a kids room. Have you considered orange and dark blue? These colors are as striking and visually interesting as black and white. You can also do candy stripes on the wall or colorful rugs. You are not restricted to bars and stripes. Consider hot pink and alligator green spots. You can find funky wallpaper and even wall decals that let you stretch your imagination for your kids room. I find creative wall decor or kids room inspiration from --strangely enough--dorm decor sites or pin boards on Pinterest. There may be crossover for dorms and kids' room colors because of limited storage.