As a follow-up on the previous conversation:
https://discuss.kakoune.com/t/is-it-possible-to-highlight-whole-lines-with-a-regex/
I have published a plugin to colorize buffer regions in Kakoune. The plugin allows multiple colors across filetypes and across regions of the same buffer. The plugin also allows the initial and/or final lines of a region to be customized separately. For example:
Details here: