I am looking for a juvenile fiction book, written sometime in the 1980s. The premise is that people of privilege live indoors and never see the sun; the main character is a very haughty, arrogant teenager who lives indoors. A big deal is made about how pale and fat these people are. Somehow he accidentally ends up outside — I feel like he falls down a garbage chute — and ends up finding a village of families who live outside. After a while, he loses his arrogance and begins to enjoy his life outdoors. Eventually he makes his way back to his home, and I distinctly remember people shunning him because he has gotten muscles and a tan. I read it in the fifth or sixth grade, so it would have been aimed at children ages 10-12 or so.

The cover of the book shows the back of a pale bald boy, dressed in robes (they may be purple or blue?), running down a hallway. Thanks for the help!