In the movie by the same name(and presumably the book as well), there is a scene where two ladies, Shug Avery and Celie, are walking through a field of tall beautiful purple Cosmos. And during their walk, they were talking about that even the flowers do things to get noticed. In this case, the flowers were purple. The color purple(not the movie, but the actual color) has signifigance to clockwork, as when people are needy of attention, their 'field' or 'presence' is purple. Though this isn't always something plainly obvious(the color that is), Clockwork by his nature will always try to attend to people in need of a bit of love.
(As an aside, oocly, I like to think that the world can be made a lot smoother with just a small bit of "color purple" ... people need attention, and will do stuff to get attention... and giving a bit of attention to those people makes them happy. So, next time you see someone doing something, like trying to show you something, or just talk to you, pay attention, for just a few moments, and let them have some attention, because if they could, they'd have purple flowers to get attention, but since they, don't, they have to show off, just a bit, some other way.)