It looks like you need to define it in code2color. The documentation here lists the background.
Syntax highlighting of source code is possible through an included
script code2color which is derived from Peter Palfraders code2html
script or an external program (pygmentize). The script code2color is
written in perl and has colorizing support for the languages ada, asm,
awk, c, c++, groff, html, xml, java, javascript, lisp, m4, make,
pascal, patch, perl, povray, python, ruby, shellscript and sql.
Syntax highlighting and other methods of colorizing the output are
only activated if the environment variable LESS is existing and
contains the option -R or -r or less is called with one of these
options. This guarantees, that instead of literal escape sequences
colors are displayed. The detection of the -r/-R presence at runtime
is rather dependent on the operating system and may not work in all
cases.
The script lesspipe.sh needs a lot of helper programs that may or may
not be installed on your computer. Therefore you should download the
tarball lesspipe.tar.gz and use configure to customize lesspipe.sh for
the local computer. A preconfigured lesspipe.sh for Linux is provided
as an example only. There syntax highlighting is switched on. The
code2color script does the colorization, but can be replaced by an
external program (pygmentize)
To get support for newer file types an additional magic file (for use
in the file command, e.g. in ~/.magic) might have to be created. In
that case the environment variable MAGIC has to be set and has to
contain both the system magic file and your personal one. Example:
MAGIC='/usr/share/file/magic:/Users/myaccount/.magic' export MAGIC