Redsnail is correct.
You can be a Captain in Australia and exercise the ATPL privileges provided you pass one of the colour vision tests which can include the control tower signal gun test.
However, even if you fail all colour vision testing, your medical will include the restrictions 'not valid for ATPL operations' and 'holder does not fully meet the requirements of ICAO convention Chapter 6 of Annex 1'. This effectively means you are restricted to Australian airspace only and you can only operate up to CPL licence privileges. This still allows you to fly any single pilot aircraft as pilot in command (which includes high performance turbo-props such as King Air's) and also allows you to operate as a First Officer in any multi-crew aircraft including passenger jets.
There is a further legal challenge currently underway in Australia with court hearings expected early next year to challenge this final restriction. There are now a significant number of pilots in Australia with many thousands of hours experience who hold this ATPL restriction and are denied the opportunity to become Captain's, despite impeccable safety records which indicates that their CVD does not affect the 'safe performance of their duties'.
Arthur Pape is indeed your friend with this and is also heavily involved in the aforementioned case, which has the potential to set an important international precedent. It will also further expose the far worse discrimination being experienced in other countries. You can contact him via the CVDPA website.
For those interested in the background as to how Australia arrived at the position it is now, the below aeromedical article is also a worthwhile read:
Colour Perception Standards in Aviation: Some Implications of the AAT Decisions Regarding Colour Perception and Aviation