Fix parsing of the --no-color option.

The `--no-color` option hasn't worked for a while (since #601, my fault). This fixes it.

The solution is simple but will have to be changed if we ever introduce a `--[no-]something` option. An alternative solution would be to do that now and change it to `--[no-]color`. I prefer this way.

We don't have any specs for coloring and I found it difficult to add any.