What influences build log highlighting?

Hello-

I'm working on writing a Rake script. Our build is such that we won't be using any off-the-shelf build tools, so I'll be writing out a custom build log. How can I write it out in a way that errors are highlighted, as they are when I'm using something like rSpec (i.e., errors are red, ignored tests are orange, everything else is black)?

Regards,
Eric