Ok. There are 2 Main coilcoaters in NZ.
NZ STEEL who make Colorsteel
PCC who make Colorcote.
Both of these produce a coloured coil for rollforming.
Company’s like Dimond, will rollform this coil into profiles. Such as Corrugate,5 rib, 6 rib, styleline etc.

Your standard grade “coloured” steel will be fine to reroof your house. Being 1km from the sea should be ok. But it pays to ask for warranty check on your address and this will provide a recommended grade for that address.
Zincalume basically is your “non” coloured product.
This will also be fine for reroof, based on warranty check, as long as you are happy with a plain product.
Contact your local rollforners. Such as Dimond. They will provide recommended installlers to provide you with a price.

Hope that enlightens things a bit. It can be confusing

I am a former Plumber/Roofer and I think there is a lot to be said for a factory coating especially as you are close to the water. I dont think that you can get anywhere near as good coating by using Zincalume, then spraying or brushing on a paint. Being close to the water I would ask them specifically to touch up any cuts in the sheets with aerosol paint prior to laying, as these areas will corrode first. I suggest you keep the roof clean to help preserve the coating including gutters. 

I went with color steel which is fine but I got the regular thickness which dents to easily when walking etc which sucks..
The slightly thicker one is not much more money and I would get that in future for sure.
Not up to date with pricing however.

Guess there's not much difference between the 2 brands? Just got a quote back colorcote was more expensive than coloersteel for top to range stuff.