I would start here
https://www.mobileread.com/forums/sh...d.php?t=371967 for the palette switcher plugin. Next stop possibly
https://www.mobileread.com/forums/sh...d.php?t=372047 for the palette config plugin. And last take a browse through
https://www.mobileread.com/forums/sh...d.php?t=359611 for various color palettes you can use or change at your preference.