Nintendo's RGB palettes have typically been what many would call "crap". Probably the NES Classic got closest. Wii VC was way too dark. None of them too horribly accurate.
I don't think they used PCX along the way at all. At one point, they'd digitize graphics by using LEDs to scan filled-in graph paper, one tile at a time. I think the closest Nintendo ever got to actually having an official RGB palette for the NES in the old days was the RGB PPU palette (which was very, very different from the colors output by the composite PPU).
The NES PPU is fairly well understood, and palettes can actually be calculated based on that (as opposed to some of the user-created palettes done with visual analysis). All of Nintendo's RGB palettes (AFAIK) are known and dumped.
I don't think they used PCX along the way at all. At one point, they'd digitize graphics by using LEDs to scan filled-in graph paper, one tile at a time. I think the closest Nintendo ever got to actually having an official RGB palette for the NES in the old days was the RGB PPU palette (which was very, very different from the colors output by the composite PPU).
The NES PPU is fairly well understood, and palettes can actually be calculated based on that (as opposed to some of the user-created palettes done with visual analysis). All of Nintendo's RGB palettes (AFAIK) are known and dumped.