This question already has an answer here:
I'm trying to figure out how to customise some of my folders' sidebar icons that are using custom ICNS icons via "Get Info". They're basic "Documents", "Downloads", etc. folders that I've replaced with my own on a secondary drive.
Currently running El Capitan 10.11.6.
An option that doesn't require an external app would be ideal. Can Dropbox's method be replicated? Thanks!