Watch this science video tutorial from Nurd Rage on how to make silver different colors by electrochemical anodizing. Without using paint, you can give a silver surface various colors by anodizing it.
WARNING: Anodizing solution is corrosive, so wear gloves at all times when working with it. It is also somewhat toxic, so keep it away from children and pets too.
To make the solution, just mix two tablespoons of sodium hydroxide (lye) and one tablespoon of sulfur with half a cup of water (~100mL). Stir for about ten minutes until the solution turns orange. Then filter the solution to remove excess sulfur.
You can get sulfur from online sources (including eBay) or from some drugstores. Sodium hydroxide is the primary component of some types of drain cleaners. But read the label carefully, drain cleaners come in many types and a lot of them don't have sodium hydroxide. You can also buy sodium hydroxide online, it's sold for making home biodiesel or homemade soap.
After you made your solution, thoroughly clean your silver article and place it into the solution. Attach the positive terminal of a 3v battery to the article and dip the negative wire into the solution. Move the negative wire around the solution to give the silver an even coat, or keep it in a single spot to apply rainbow effects.
What's happening is the electric current is oxidizing the silver and causing it to pick up the sulfur dissolved into the solution. As it does this it thickens and alters the way light reflects off the surface. What color of light is reflected is determined by how thick the sulfide layer is. The thickness of the layer is determined by how long you anodize it. So you can control the color by controlling the time you apply the current.
The process can be used to tint silver items to give them an antique look.
Brought to you by one of WonderHowTo's favorite scientists NurdRage.