At Urban Outfitters Bike Shop, you can. You don’t have do any fancy welding, just go to their interactive web site and go from there. You start with a pattern like this:
And they help you with designing it yourself. This model, the Plato Dutch Diamond, comes in around $399 for a fixie/1-speed. I have a bike like this (not from them), and I love it. There’s even a random option if the choices overwhelm you. Now you can have that 5 colour bike you always wanted. 🙂 Or for that matter, a basic black model with a touch of red. Whatever, you have lots of flexibility. And in the end, a bike all of your own.