Best time to come? Last week. Or next week. Or maybe the end of the year. No one knows. Though most companies seem to be close to, or fully staffed for the season.
Helicopter pilots? No idea. Best to contact the company directly. They can give you a better answer, plus they don't hire the same way.
Colour vision deficiency? No idea either. But read back a few pages and see that you use your home medical to start with anyway.
And personally, I don't have an EASA or FAA licence...