And note that isatty() works on a file descriptor, and that you might be outputting to both stderr and stdout, and both, neither, or some weird combination might be a tty. (i.e., you need to check for the file descriptor you're going to output to.)

Some programs will check if stdout is a tty prior to writing to stderr, for example, which means that if you're doing,

  foo | bar

foo's stderr will go to the tty, but would lose coloring, for example. For example, `babel`, a JS transpiler, loses the color in its error messages when you pipe its output.