Ever wonder how a metal object has a colorful patina that doesn't really look like paint? It's probably been anodized if it's aluminum or titanium. One interesting property of these anodized metals is that the color differs depending on the voltage used during the process. KEYBAR shows us how it's done in this cool demo.
Surface finish can also affect the appearance:
It can also be applied precisely with a needle:
Image: YouTube / KEYBAR