Thanks both.
I use Kobo night mode for years now, yep. Sorry if I wasn't clear. My question was more for the other brands.
I have installed KOReader on my glo HD and found it nice too. So I'll be good to go for either a Pocketbook Inkpad 3, or a Kobo Aura One / Forma .
No Kindle for me..... I need an open reader. I don't want to have anything to deal with Amazon's ecosystem.
