It would be fantastic if I could to set the colour of certain folders to aid in visual separation and navigation. Such as /public to red, /resources to blue. I'm used to Photoshop's ability to do this for layers/groups/folders and it makes it easier to navigate when you have the folders expanded and where the break points are to collapse/expand etc. My app is starting to get big and I'm wasting valuable seconds hunting files down! Ctrl+P search helps, but still, I'm a dumb human!
Surely in this magical, fully editable program there is a way? I can't find it if there us, so here I am...
As of the most recent version of Sublime Text (currently development build 3154) there is no API available that would allow core Sublime or a third party package to style the sidebar in this manner. The only visual changes that can be made are theme related, which cover the side bar and it's layout/display as a whole without the ability to target specific files or folders.
You're not the first person to want that particular feature, though. The issue tracker has an issue/feature request for Sidebar API enhancements that covers this proposed addition.