How can I colorize/propertize the lighter of a minor mode in the mode line?
Refer to the manual:
(elisp)Properties in Mode
Or in the online manual (which is always for the most recent stable release of Emacs): https://www.gnu.org/software/emacs/manual/html_node/elisp/Properties-in-Mode.html
I think there's no point in quoting an excerpt here -- you need to read the whole page.