kindle app on my hdx offers white, sepia, or lilac. lilac has been there for a couple of years at least. same place as where you set font, text size...
kindle for android on a non amazon device
may have the same options
in bookari, i was able to match the lilac after much trial and error. and my night theme in bookari is done by moving the colour select a littlw way out of bottom left corner for a neutal grey. I cant get that same level of neutrality with the RGB sliders in moon and I
still can't comprehen how they interact with the choice of theme/background image. another bookari annoyance is that the theme colours are not stored in the .db with all the other book settings, so there is no way to back them up and you lose them if ever you re-install the app or move to a new tablet. I asked bookari and also spent ages looking for them with file explorer... no joy
ps
lilac - aka green- can be seen here
http://teleread.com/want-use-amazon-...en-background/
I have not been able to re-create that shade in moon+