thats a switch to kindlevncviewer... so pass -dithered to the kvncviewer instance when you call it.
/mnt/us/kindlevncviewer/kvncviewer.sh -dithered 192.168.2.1:1 &
something like that (I didn't check that, might expect to be INSIDE the .sh - have a look in there if that fails)
the above is
not a system-wide thing.
if you want something system-side then you want the
https://www.mobileread.com/forums/sho...d.php?t=206917
Kindle DX Kernel Module for Contrast
and then
https://www.mobileread.com/forums/sho...0&postcount=41
Hope it helps