Players' efforts over the years to get Wimbledon's "all-white" clothing rule relaxed got a boost on Thursday when Roger Federer said he thought the policy as it stood was "quite extreme".

Federer, whose remarks carry more weight than some other players because as a former champion he is a member of the All England Lawn Tennis Club (AELTC) that runs Wimbledon, said he did not object to white clothing.

But he said he thought the AELTC was pushing it by ruling out garments that are less than pristine white -- which could come from repeated washes -- and he spoke wistfully of the days when players like John McEnroe and Boris Becker wore striped T-shirts and colourful headbands that are no longer allowed.

"I mean, that it's all white, we're all for it. We get that. I just find it quite extreme to what extent it's got to be white. We're talking white like it was in the '50s. If you look at the pictures then, it was all white," Federer told a news conference after his second-round win over Sam Querrey.

"The thing is, when I came on tour, when I was watching on TV, I still have the pictures in my mind where (Stefan) Edberg and Becker and all those guys, they had more colour. There were iconic T-shirts, iconic moments, I thought," said Federer, who was ordered by Wimbledon officials not to wear orange-soled Nike shoes on court in 2013 when he was the defending champion.

He said when he joined the tour the garments were "90 percent" white but could still have some light blue or black.

"But then it got to a point where stripes would be borderline here. I find that a bit of a pity because you can't do anything with it. No cream colour, no this, no that, fine.

"I would still be in favour of loosening it up a little bit. But, then again, it is what it is. You know, I'm happy, I'm proud to be here. So whatever, it's okay," he said.

The undercurrent of resistance to the all-white rule this season has included a woman player wearing a black bra which she concealed by wearing a white one over it.

Then American Bethanie Mattek-Sands, who is ranked 158th in the world and whose headshot for her WTA profile shows her with her hair died turquoise and lime green, turned up the volume after she upset seventh-seed Ana Ivanovic on Wednesday.

She said the all-white rule had "gotten a little excessive" and was disappointed that she could not wear tennis skirts she'd brought with coloured underwear.

"It was funny, because I was actually googling some players like when John McEnroe played, Arthur Ashe, they had colour everywhere. They had colour on their sleeves, big stripes, they were coming out in coloured jackets. So I feel it's actually gotten stricter," Mattek-Sands said.

Given a choice, she said she would almost never wear white, and had not worn a white gown for her wedding.