Has anyone ever told you that appearances don't matter? Well, you'll have to forget that for now. In a novel where characters are searching for identities they can believe in, appearances are, like, super important. See, characters in White Teeth use what other people tell them about their appearances to understand how the outside world views them. The narrator gives us really detailed accounts of characters' appearances too, so we are also asked directly to think about what it means for a character to look a certain way. All this talk about looks might not leave you feeling good, but it's pretty hard to escape—in our culture at large, and in this book.
Even though Millat and Magid are twins, people pay much more attention to Millat's appearance than to Magid's—Millat trades on his appearance while Magid presents himself as a brain.
While it might not be fair to judge people based on their appearances, people do conciously manipulate their own appearances to send messages to the world around them.