Doesn't work on Xfce either. On a virtual terminal thingy (ctrl-alt-f1) it shows a grey background with white text. I suspect blink is only implemented on the Mac's terminal, not in Linux-land.
...Lord, when did I get so old? :/
https://en.wikipedia.org/wiki/ANSI_escape_code
It's definitely a terminal thing. The "bug" in git is that it doesn't strip out the control characters or reject the commit if the commit message contains non-text data.
Anyway, they default to "linux" for more than a decade.