The Enterprise 64 or 128 Home Computer apparently had a palette of 256 colors.
However, that is pretty unusual and doesn't fit evenly into the typical 3 channels for RGB. Wikipedia doesn't provide any additional information.
So, were the available bits per channel unevenly assigned and thus not equally represented in the machine's color space?
Or was there an additional intensity channel (RGBI)?
Or did that computer use an entirely different color model than RGB?