The prime minister's hair isn't the only shade of grey he's thinking about this week.

Prime Minister John Key has turned his mind to the Fifty Shades of Grey film, which is scheduled for release in New Zealand today.

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But moviegoers shouldn't expect to turn to their neighbour in the cinema and see the prime minister - he'll be watching that one with just his wife, Bronagh.

Key said on MoreFM this morning he had seen the movie trailer but, as for watching the full film, "might have to restrict that to the TV at home, I think."

His expectations may have been lowered slightly by advance reviews of the movie, however.

"They said it takes 40 minutes to get to the first sex session."

Key seemed surprised that "the whole movie only includes 11 minutes of 'forbidden fruit'."

The prime minister claimed his interest in the movie was because he tried "to keep well-informed for the country."

"You know, I do my best for people. It's not always appreciated, but I do my best," Key joked.

It's been a week of unusual conversations for the prime minister.

On Tuesday NZ First leader Winston Peters accused Key of dying his hair, which Key yesterday responded to with "there's no dye on these locks, baby!"

Peters countered with "well, why don't the curtains match the carpet, then?"

The prime minister rose in the House to raise a point of order, good-naturedly taking offence "that the member is telling New Zealand that he's seen my carpet!"