No it isn't. The 256 colour system is based upon a palette, too. Indeed, in almost all terminal emulators it is the same palette as the AIXTerm 16 colour syst

No it isn't. The 256 colour system is based upon a palette, too. Indeed, in almost all terminal emulators it is the same palette as the AIXTerm 16 colour system, which just uses its first 16 entries. (They could be theoretically two different palettes. I know of no terminal emulator author who has implemented it this way. I thought of doing so, but even I didn't.)