So I've got this touring bike in a lovely shade of blue. And I want to extend the color scheme. Any suggestions on how/what to use to turn metal colored parts blue? I was hoping for something that wasn't paint.

anodizing?
powdercoat (as opposed to traditional paint)?

Aluminum can be anodized different colors. Some steels can be heat treated to produce many shades without wrecking the crystalline structure. Try applying the blueing (sp?) used on shotguns and rifles. Not as durable as anodizing. Talk to an electroplating shop for some ideas.

wrap it in foil.

i've wrapped an entire tallbike in tin foil, but i'm sure you could get coloured foil.

poor aerodynamics.