Quotes were interpreted by configure and $NO_COLOR was interpolated at
configure time, leading to incorrect script execution. Brackets were
also removed because of m4 expansion.

By switching to single quote string, we can better describe what needs
to be printed and what needs to be evaluated.

The m4 expansion problem is solved by escaping the whole string in a
bracket block.

The `echo` command is also changed for the more portable[^1] `printf`.

[^1]: https://unix.stackexchange.com/questions/65803/why-is-printf-better-than-echo