…and you can only pick from those pairs!
Dark-green/dark-magenta dither is not an option! But, that was the dither pairing that the artist was going for, so... they just drew the dither *manually* across a ton of commands! Easily way more "expensive", in terms of bytes-on-disk than a palette command, but i'm sure there were other "risks" involved with updating the engine itself to support that.
By PQ2 you start to see some of the PALETTE_UPDATE commands (which alter single palette entries)