[wezfurlong]

I don't recall where I saw it, but my understanding was that : was in the original spec but one of the early implementors (Konsole?) misread it and used ; and that erroneous form is what took off, and here we are today.

[follower]

I'm guessing it may have been one or both of these `xterm`-related documents:

* <https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h4-F...>

* <https://invisible-island.net/xterm/xterm.faq.html#color_by_n...>

More details in my other comment: https://news.ycombinator.com/item?id=35157058