There are at least 3 different ways of expressing colour as covered by https://en.wikipedia.org/wiki/ANSI_escape_code#Colors, and given the wide propensity of newer terminals to misidentify what they are (I know I have some additional checking in my shell startup to unbreak things if needed), and/or bad termcap/terminfo settings on older systems, sending terminal sequences that are apparently supported but are not happens surprisingly often (enough such that I've made sure to always install two different terminals which use different rendering backends, e.g. xterm and VTE).
