You could get a purple skin for an Air. They don't add any bulk and will protect the case from scratches.I'm really wondering if there will be a small "color"-upgrade soon for the existing Mac Book Air. It was rumored some month ago and my daughter would love a purple Mac Book Air for school.
They now have a "BYOD"-policy (bring your own device) so any student has to bring his own notebook.
But school starts soon, she probably has no choice but the existing ones.