This thing was made with Tinkercad.
If you have a Generation III Prius (2010-present), you can pop off the UGLY wheel covers to release the alloy beasts underneath. Except - you'll have a hole in the center of the wheel that begs for a decorative cap. This is precisely measured from the Toyota part number 42603-52110 (pictured).
This has the iconic power symbol embossed in the top of the wheel cover, as found on the power button of your Prius. More info: http://en.wikipedia.org/wiki/Power_symbol
More photos; http://www.flickr.com/photos/theschlem/sets/72157632696775253/with/8449866372/
Also fits Yaris, Vios
These and other center cap designs, for GenII and GenIII are available through Shapeways:
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I'm not sure how these WILL print on an extruder type machine- I am sure that they will need support. Experimentation is in order. The photographs are of sintered-nylon samples printed by Shapeways.
Disclaimer- you print and use this part at your own risk.
Painting ABS is fairly straight forward: just rough it up a bit with some fine sandpaper and hit it with a few light coats of your preferred body paint. No primer necessary.