Blargg's NTSC filters emulate NTSC artifacts such as the vertical jaggies and chroma bleed. These filters have been available in many emulators for quite a few years.

Also note that Blargg's filters are efficient integer-only CPU filters, as they are fast enough to not need a GPU.

http://slack.net/~ant/libs/ntsc.html (main page)

http://slack.net/~ant/old/ntsc-presets/ (lots of example images)

http://slack.net/~ant/old/ntsc-vs-palette/ (examples specifically about the color-"correction" that happens when using NTSC)