Vignetting can greatly enhance portraits with solid color backgrounds. Here is a very quick way to add vignetting. After you are done with editing your image, go to the Lens Correction filter. Play with sliders to change the effect as you like. This filter is actually great for removing vignetting and wide angle distortion of [...]

The lomo effect in this tutorial mimics the funky retro-looking colors, high contrast, and strong vignette of lomo cameras. First you add a Levels Adjustment layer and choose the Red channel. Then increase the contrast. To get the colors back, adjust the Green channel as well. Then add a vignette and change the blending mode [...]

Watch this video lesson and learn how to make a Vignette with Curves. It is just one of many methods of making a Vignette but it gives more contrast to the background.