In a lot of the older systems (this was VERY common on the NES and SNES), the designers utilized some very heavy-handed dithering under the assumption that the dithering would be blurred heavily by both the CRT and the NTSC encoding. As these images demonstrate, the colors are incorrect if you skip emulating the NTSC chroma bleed.
It was also very common to assume there wou9ld be darkening from the scanline effect on arcade machines, leading to brightness problem in the emulation of some ames.
http://slack.net/~ant/old/ntsc-vs-palette/
It was also very common to assume there wou9ld be darkening from the scanline effect on arcade machines, leading to brightness problem in the emulation of some ames.