I Just Wanted Emacs to Look Nice — Using 24-Bit Color in Terminals
chadaustin.me
TL;DR: Explanation of why the escape sequence for 256 color and 24 bit color modes are weird and can vary. \E[38:5:_n_m is technically the correct form for 256 color, but \E[38;5;_n_m is the form terminals more widely support.
I saw this on Hacker News today, and found the article interesting because I'd recently seen a Terminal Guide page on 256 color that mentioned how terminals support different versions of the codes (with semicolons being the most compatible). Semi-relatedly there's XTerm's criticism of Gnome Terminal and VTE (which is talks about compatibility in general).
I could feel my grey beard growing long as I read that.
If you're using emacs, stick to the GUI unless you have good reasons not to. The GUI is more or less a smart terminal. You're missing out on a lot of features if you opt for the terminal.