There are 3 icon types available for folders: collapsed, expanded and symlink. Take a look at file_system_entry in https://www.sublimetext.com/docs/themes.html
Then in Preferences > Browse Packages > User, create a new file and call it Default. sublime-theme (be sure that the extension is in . sublime-theme). Then you can change the sidebar color by changing the RGB values of “Background color” .
How to change the color of right sidebar (miniMap) in Sublime Text 3 · Check your current default theme name. Preferences > setting - Default. Find theme.
i suggest that you could color the folders and files. so that you could mark them as relelvant, and they could stand out for easy distinction. the colors ...