To play at Wimbledon, even your underwear has to be white.
The All England Club has rules about how much colour can be worn on court, and a few junior players seem to have run afoul of the strict standards this week.
According to the BBC, the doubles team of Zsombor Piros of Hungary and Wu Yibing of China were given white underpants and forced to change before their match on Wednesday.
When the boys returned on court from the locker room, they walked to their chairs and put their darker undies into their tennis bags.
On Thursday, a different player tugged at his shorts to reveal the top of his underwear to an official while standing at the net before the match.
"It is our preference that any issues regarding the 'all-white' rule and undergarments are discussed and dealt with between matches," the All England Club said in an email.
"Unfortunately, we have been made aware of a couple of instances where this was not the case, but we will ensure this happens in the future."
Wimbledon tightened its all-white clothing policy in 2014, and even Roger Federer complained about it that year. He harkened back to the days when past champions such as Stefan Edberg and Boris Becker had some colour in their clothing.
But All England Club chief executive Richard Lewis said in a statement at that time "the rule is almost entirely in white."
Earlier in the tournament Venus Williams caught the attention of officials when her bright pink bra straps became visible on the opening day.
Following a rain break, Williams returned to court in a different outfit that satisfied the dress code.
Williams, who has since gone on to reach the women's singles final, reacted to questioning about her clothing at a press conference by saying: "I don't want to talk about undergarments.
"It's kind of awkward for me. I'll leave that to you. You can talk about it with your friends. I'm going to pass."
Meanwhile, Austrian teenager Jurij Rodionov became the latest player to breach the dress code when he was reportedly instructed to change underwear.
The 18-year-old beat Australian Blake Ellis on Court 18 in the boys' singles on Thursday but only after having to change clothes before the match.
After identifying a possible problem, match umpire Phil Lodge asked Rodionov about the colour of his underpants, and when it became apparent they were dark blue a supervisor was called.
According to the New York Times, supervisor Lucy Grant told Rodionov: "This is the problem we have: If you're serving, the shorts could become visible."
The newspaper said she then requested for white underwear to be brought to the court.
Rodionov left the court to change, before returning to earn a 6-3 6-7 (7-4) 6-3 victory that sets up a match on Friday against French top seed Corentin Moutet.