millonario
The Cathay medical staff will do a Ishihara colour-blindness test with you, and if you pass that will be the end of it. I'm not quite sure what they would do if you happen to get the questions wrong.
Having said that, it is quite possible that Cathay and the CAD have different requirements towards candidates' health and medical history. While you can find out about the CAD requirements online (I was told that the CAD requirements for an initial issue Class 1 medical were very similar to JAA, if not entirely identical), it would be much harder for you to have an idea of what Cathay wants. I'd suggest you apply for the cadetship regardless. You never know until you try.