Vignetting is often used to darken parts of an image (usually the edges), thereby drawing attention to the middle which remains brighter. The classic way to vignette is to simply add a Levels or Curves adjustment layer set to the layer blending mode of Multiply, and then paint on the layer mask with a large, soft black brush where the darkening is not wanted.
Another way to accomplish this is to instead use a Photo Filter, and paint black on its mask. Here is the starting image of Laurel:
A Photo Filter was added, set to Deep Blue with the Density at 68%. On the mask, a black brush was used to paint away the blue over Laurel and the lamp on the left:
There is nothing that says color cannot be used to vignette an image. In this instance I like how the bluish edges of the image contrast with the warmth of the lamp and Laurel.