The campaign first started in Nova Scotia where a group of high school students organized a protest to support a Grade 9 student bullied for wearing a pink shirt.
(Another campaign claiming the same origin, Pink Shirt Day, is marked on Feb. 25.)
Police departments got into the campaign in a big way. Some went with the traditional pink shirt.
Toronto police officer Luke Watson took it a step further, dying his hair pink for the occasion.
The Day of Pink is marked in many school boards across Canada. Greg Pearson is a vice principal in Ontario's Peel District School Board.
The Canadian Centre for Gender & Sexual Diversity is one of the organizations behind Day of Pink. They posted this shot from Ottawa.
Actor and self-described "irritating guy from Stargate Atlantis" David Hewlett donned a pink bandana.
One of the most retweeted photos on the #DayOfPink hashtag came from the Washington Capitals' Eric Fehr.
Some politicians got into the spirit of the day, including the American ambassador to Canada.
Toronto Mayor John Tory also tweeted about it.
However, it was the choice of another political figure, Laureen Harper, as the face of Day of Pink that has led some LGBT activists to boycott the campaign.
Harper wrote an open letter posted on the website of the Canadian Centre for Gender & Sexual Diversity about why she would be wearing pink Wednesday.
For some activists, choosing the wife of Canada's prime minister was a mistake that undermined the message of the Day of Pink.
Queer activist Ariel Troster expanded on this tweet in a post on Storify. She pointed to a Conservative senator's amendment of Bill C-279, the transgender rights bill, as one reason for her boycott.
"Conservative Senator Don Plett was responsible for inserting a poison pill into long-awaited trans human rights legislation," Troster wrote.
Some people had reservations about Harper's role in the campaign, but said they would observe it nonetheless.
(Note: The CBC is a sponsor of the Day of Pink campaign.)Suggest a correction