From reading the protocol "spec" I do not see how it could be used to transmit 32 bit color (or higher). The spec describes 8 bit indices into a palette. I have seen no sixel tools that are able to output 32 bit color, or any sixel terminals that can display 32 bit color. But I could be misreading it. I haven't dug through all the code so if someone could show how this could be done, then we could start to change those sixel implementations to do the right thing.