On 24.05.2016, at 14:00 , Igor K <me@igorkozlov.me> wrote:

I think you're right. I cant remember what editor I saw which uses this... maybe Atom or Sublime, and also vim with a plugin.

Probably you're talking about this plugin: https://github.com/abe33/atom-pigments
AFAIK, there's no way to implement this without modifying TextMate source code.

IntelliJ Idea displays a tiny coloured square in the gutter next to any line (not just CSS) that contains a color-value:

I think TextMate bundles could be made much more powerful by allowing to modify the gutter a bit.

* paint into a rectangle in the gutter (per html?)
* act on click and hover there (including screen coordinates maybe)