As you can see in my eink code (GMLIB), you will see that the 8-bit eink framebuffer must have a copy of the 4-bit value in both the top and bottom half-bytes. More than 16 colors are created with dithering. You can copy a framebuffer that contains a screensaver image (or special offers ad) , then load it into an image processing program and do histogram analysis on it. You will see 16 spikes, showing that it is really 4 bits duplicated as described above.
The eink driver GPL source code has comments saying that NOT having duplicate half-bytes in 8-bit framebuffer mode can have unpredictable hardware-dependent results.
EDIT: As you can see in your color map, each color value is just 0x0 through 0xf, repeated into each half-byte of the color map word size. 16-colors, even in 8-bit mode. I have code that dithers 256 color to fit into either 4-bit or 8-bit framebuffers, and works in all modes (main and diags) on all the eink kindles.
Check out the
newtrix demo for details and sample code:
https://www.mobileread.com/forums/sho...d.php?t=176802