Only thing I can imagine is that each black & white pixel becomes a red or green or blue subpixel taking the dpi down to a third unless they have some subpixel hinting.
That’s exactly how it’s done. They apply a sticker to the screen with little red/green/blue dots aligned to the eInk pigments. Every “pixel” can then be turned black or coloured. It looks pretty washed out, but works.
In this video you can see Jerry peel off the sticker at the end:
