List Highlighter helps you focus on what you're working on.
Trello boards can fill up with multiple lists pretty quickly. List Highlighter helps you make the important ones stand out. You can change the list background colour, count cards, and break up long lists with headers and separators.
It's been a long time coming, but with version 4 you can set your own highlighting rules, based on any list title text you like.
For more information, visit the List Highlighter homepage.