We're invoking a VM via Qemu running Debian 10 and the default TERM is black-and-white. Supporting only plain text and bold text. As such, tput informs us some of the colors are unavailable.
It prints no error message but exits non-zero. I didn't realise before that this command can exit non-zero under what I consider normal conditions (e.g. falling back to no colors), but https://linux.die.net/man/1/tput confirms that this is normal.