Issue colors

The "colors" option allow to create nice output.
But lot of projects use it, and it create very bad output when the result is redirected to a file.

Here is 2 proposal
* add a --nocolor option (so we can use it when needed, instead of having to change to configuration file)
* add a check to only allow this option when output is a tty.

This PR is opened against, 4.3, but I will understand if you consider it only in 4.4+