I like small, clean software, that focuses on keyboard usability. PWMT, "programs with movie titles", has a nice and fast(!) PDF viewer called Zathura. The user interface looks just like Vimperator (or Vimprobable, for that matter). I like!
The config file syntax is not documented. (Only on the web site, which
is not available at the moment.) So you'll have to change the colors
within the code itself. libpoppler-glib-dev is required to
build Zathura.