Is there a .mocha file where I can specify defaults such as --no-colors?

Yes. You can create a file ./test/mocha.opts and in the file you can specify --no-colors.

See mocha.opts on Mocha Doc for more information.

Mocha recommends mocha --config=.mocharc.json.

There are new formats too, like yaml. See some examples.

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Old answer:

The default is ./test/mocha.opts. You can pass a custom path with the --opts parameter :

mocha --opts ./mocha.opts

Useful in case you don’t store your tests in test/ folder, but next to code files, for example.

Any name and extension seems to work, so you can even do mocha --opts .mocharc if you want it to go well with .jshintrc, .babelrc and the like.