Basically the 32u4 processor (the kind used by an Arduboy) has a certain number of connections with different names (each connection is called a ‘pin’) and those would have to be connected to the PEX (the group of pins at the top of the Pokitto) in a way that’s suitable for using the SPI protocol and so that the other pins can do their jobs properly (e.g. 6 pins for the buttons, some pins for sound and some pins for the LED).
Effectively the hat route would mean that the hat itself is an Arduboy without the buttons, screen, speaker etc (i.e. it’s literally just the processor) and the Pokitto would be reading and writing to the pins to pretend to be the buttons, screen, speaker etc.
That might be a bit difficult because the Arduboy screen is 128x64 amd the Pokitto screen is 220 x176, so it’s probably going to be a bit awkward to upscale without looking stretched or uneven.
As for colouring, the hat approach would be different to the approach we were discussing on the other thread that introduces colour.
For the hat approach, you can do stuff like displaying lit pixels as green instead of white, but more than two colours would be difficult.
With the approach we’re discussing in the other thread, the game’s original source code would be needed because the game would be recompiled to run directly on the Pokitto, which also gives us more freedom with other things because the Pokitto’s processor is more powerful.