I use the highlight package[1] that comes with Debian/Ubuntu. With that:

    highlight -O ansi file.ext | less -R
    highlight -O xterm256 file.ext | less -R

highlight can also convert the input to other formats: HTML, XHTML, RTF, LaTeX, TeX, BBCode or SVG.

An alternative to `less -R` is the `most` pager [2].

[1] https://packages.debian.org/jessie/highlight [2] https://packages.debian.org/jessie/most