However the use of the word was widely criticised, with even Lord of the Rings star Sir Ian McKellan wading into the debate.
"I'm currently touring secondary schools in UK, attacking homophobia in the playground and discouraging kids from the careless use of 'gay' which might make their gay friends (and teachers) feel less about themselves," he said on his blog.
"So even as he supports the proposal to introduce same-gender marriages in New Zealand, I do hope John Key listens to his critics and appreciates their concern. Careless talk damages lives."
On Twitter, supporters of LGBT rights are using the #GayRedShirtDay hash tag to share pictures of the red shirts they are wearing today.
Earlier this week, the Farming Show's Jamie Mackay came to the defence of the Prime Minister on his show.
"All the kerfuffle over the gay red top was just harmless banter and for those of you who are kicking up about it ... to put it into context, there had been a lot of banter before we got on air from all the golfers outside as we were having a bit of a lunch and one thing lead to another, because we were giving the Prime Minister a bit of stick about putting like Bronagh, so I thought he'd just get some of his own back.
"It's all been a storm in a tea cup."
- nzherald.co.nz
