Jud McCranie wrote:

... Although we found a color of Hardie board that we like, he says
you still have to paint it

One Hardie person repeatedly answered my email question "How long will
it last if it isn't painted?" by saying it's only guaranteed if painted
within 6 months, they've never tested it without paint, and so on.

Another guy at their toll free number said it is somewhat porous to water
and if it's unpainted it may be damaged by freezing and thawing and water
that seeps through to the other side may damage whatever is underneath.

Nick