You can add this function to your .bashrc
(or the configuration file of the shell your using instead):
man() {
LESS_TERMCAP_mb=$'\e'"[1;31m" \
LESS_TERMCAP_md=$'\e'"[1;31m" \
LESS_TERMCAP_me=$'\e'"[0m" \
LESS_TERMCAP_se=$'\e'"[0m" \
LESS_TERMCAP_so=$'\e'"[1;44;33m" \
LESS_TERMCAP_ue=$'\e'"[0m" \
LESS_TERMCAP_us=$'\e'"[1;32m" \
command man "$@"
}