Do you mean that in NZ both forms of the word are acceptable for everybody or just newcomers? I know I've always been taught UK English spelling in school and teachers always took marks off if I spelled it "color."

I'm thirty-two, and like you, when I went to school, "color" would have been marked as wrong. Now, though, it is accepted as an alternative, particularly at our primary, or elementary, level. "Colour" is still taught, but if a child spells it "color", they are unlikely to be marked down for so doing, although they may be advised that it is not considered standard spelling in New Zealand.