After years of using it, I finally just bought a Sublime license. It's about as close to perfect as an editor gets for me - fast, stable, powerful, extensible, portable, and very low cognitive overhead. Kudos to the Sublime folks.
Just look at the contortions this little package has to go through to apply a color to portions of text: https://github.com/Monnoroch/ColorHighlighter/blob/master/Co...
It has to create and apply a fake theme merged with your current theme so colors can be added "dynamically"[1].
The ancient Emacs (I hate a hate/love relationship with it) can do this is several ways, the "modern" one are overlays IIRC.
[1] As expected, this will lead to bugs related to the users' color schemes: https://github.com/Monnoroch/ColorHighlighter/issues