I do my best to keep it to 4-5 color-coded groups because more than that, means I spend more time keeping track of pen colors than doing my work. In the past, the four I stuck with were
In a year, I read somewhere around 100-200 books. I don't have a TV and I use reading as a form of escape, and I especially like reading outside of academia. It also helps with improving my writing :)
When I'm trying to concentrate, I like having background music that's super dramatic. For some reason, instrumental music is instrumental (pun!) in helping me concentrate. Most of the songs are Korean-drama OSTs (original sound tracks), w/ a few classical music scores in the mix!
I don't categorize anything other than my "random round-ups" because it takes too much work (insert laughing emoji).