How to get color man pages under fish shell?

If you want these colors to be added only when viewing man pages, not for everything you view in less, you should set these variables in a wrapper function for man instead of putting them in your config.fish.

The whole process is to create a new file at ~/.config/fish/functions/man.fish, and inside it define a function man that sets the necessary environment variables, then calls the original man using command, passing in arguments using $argv.

This is my version of the wrapper function:

function man --description "wrap the 'man' manual page opener to use color in formatting"
  # based on this group of settings and explanation for them:
  # http://boredzo.org/blog/archives/2016-08-15/colorized-man-pages-understood-and-customized
  # converted to Fish shell syntax thanks to this page:
  # http://askubuntu.com/questions/522599/how-to-get-color-man-pages-under-fish-shell/650192

  # start of bold:
  set -x LESS_TERMCAP_md (set_color --bold red)
  # end of all formatting:
  set -x LESS_TERMCAP_me (set_color normal)

  # start of standout (inverted colors):
  #set -x LESS_TERMCAP_so (set_color --reverse)
  # end of standout (inverted colors):
  #set -x LESS_TERMCAP_se (set_color normal)
  # (no change – I like the default)

  # start of underline:
  #set -x LESS_TERMCAP_us (set_color --underline)
  # end of underline:
  #set -x LESS_TERMCAP_ue (set_color normal)
  # (no change – I like the default)

  command man $argv
end

You can set the configuration by the following commands,

set -x LESS_TERMCAP_mb (printf "\033[01;31m")  
set -x LESS_TERMCAP_md (printf "\033[01;31m")  
set -x LESS_TERMCAP_me (printf "\033[0m")  
set -x LESS_TERMCAP_se (printf "\033[0m")  
set -x LESS_TERMCAP_so (printf "\033[01;44;33m")  
set -x LESS_TERMCAP_ue (printf "\033[0m")  
set -x LESS_TERMCAP_us (printf "\033[01;32m")  

Assuming you use less as your pager, put this in ~/.config/fish/config.fish:

set -x LESS_TERMCAP_mb (printf "\e[01;31m")
set -x LESS_TERMCAP_md (printf "\e[01;31m")
set -x LESS_TERMCAP_me (printf "\e[0m")
set -x LESS_TERMCAP_se (printf "\e[0m")
set -x LESS_TERMCAP_so (printf "\e[01;44;33m")
set -x LESS_TERMCAP_ue (printf "\e[0m")
set -x LESS_TERMCAP_us (printf "\e[01;32m")

If you see \e[0m etc appearing when you view the man page, try adding this line as well:

set -x LESS "-R"

It's possible to use set_color instead of direct ANSI sequences. In fact, this allows you to use any color you want, by using 24-bit color hexadecimal escapes, like (set_color FF55AA).

set -x LESS_TERMCAP_mb (set_color brred)
set -x LESS_TERMCAP_md (set_color brred)
set -x LESS_TERMCAP_me (set_color normal)
set -x LESS_TERMCAP_se (set_color normal)
set -x LESS_TERMCAP_so (set_color -b blue bryellow)
set -x LESS_TERMCAP_ue (set_color normal)
set -x LESS_TERMCAP_us (set_color brgreen)