Jill75 and others.  My original intent on roasting a bridge, among other violin components, was to change their acoustic properties.  The color change just was an attractive adjunct.  

Alcohol based leather dyes are inexpensive and come in a variety of colors.  Dabs of oil painting pigments spread with a shop rag can also be used.

another violin accessory ripe for color treatment is the chin rest, which may be purchased in maple and boxwood.  A spray of lacquer may be needed to prevent color transfer to skin.  I have also seen maple fingerboard,