Example

# zathurarc config sample
...

# colors
set default-bg     "{{background}}"

# complementary foreground, but keep it light
set default-fg     "{{foreground | complementary | lighten(0.5)}}"

# make it a bit lighter than background
set statusbar-bg   "{{background | lighten(0.3)}}"

# make it darken by blending to a darken color
set statusbar-fg   "{{foreground | blend("#eeeeee")}}"

# use it's complementary
set inputbar-bg    "{{background | complementary}}"

Then you can add this file to ~/.config/wallust/templates and use the config file to template it. For example, zathura.template = 'zathurarc', and then define a target field, see config.