Comment by chrisdew

The current encoding is complete, so no future extensions are possible.

A fix would be to change:

  110rrrrr ggggbbbb - copy the last pixel and adjust RGB by (r-15, g-7, b-7)

to:

  1100rrrr ggggbbbb - copy the last pixel and adjust RGB by (r-7, g-7, b-7)

This leaves:

  1101???? ...

available for future extensions.