Are you sure? A quick search on Google
seems to suggest otherwise.http://www.gamesx.com/rgbadd/rgbn64.htm
For whatever reason, Nintendo opted to remove the RGB output from their N64. As near as I can tell it was a matter of a few traces from a chip (U4) to the AV output, but that's their business. According to 64 DREAM magazine, Nintendo knew RGB was the least popular method of connecting a SNES, so they didn't bother with the N64.http://www.mmmonkey.co.uk/console/ninte ... 64_rgb.htm
The N64 console doesn't officially support RGB. It can be added to some models of the console, it has to be an NTSC console (although mmmonkey has read that there is an early French Secam model that is also compatible), be careful though - as there are 2 different NTSC versions, only the earlier one is compatible.
I think the best connection method for the N64 was the S-Video cable. Well that's what N64 magazine said back in the day...