Most of the libraries stated explicitly they were not compatible with Windows unless you had other dependencies. Rainbow is no exception. One of them mentioned a graceful fallback. I wasn't able to test what happens in Windows because I couldn't get rake or rake reek to work on Windows (on the master branch without those changes). So I'm wondering if it's because I not used to using Ruby on Windows or if reek master isn't currently working on Windows. This should be investigated. 

Anyhow. I could have added the additional dependencies required for Windows but I didn't want to include Windows only dependencies by default for every user.