Redshift

see https://wiki.archlinux.org/index.php/redshift

Installation

apt install redshift # on Debian
emerge -av x11-misc/redshift # on Gentoo
pacman -S redshift # on Arch

Run redshift manuelly

redshift -l 50.78:6.11 # LAT:LON

Autostart redshift with i3

Uncomment the corresponding line in ~/.i3/config, see i3.