"Some guys knocked on the door laughing and joking and said 'you're the wrong colour to be in this job!'" Gamal Turawa told ITV News London. Video report by Sam Holder.
A black former Met Police officer whose face was painted white with shoe cleaner by colleagues told ITV News London that Cressida Dick's replacement must stamp out racism.
Gamal Turawa served with the Met for 25 years and was the force's first openly gay black officer.
During his early years Gamal said racist behaviour was often dismissed as "banter" and he had to go along with it to "fit in".
"It's micro aggression, banter, which when I initially first joined I took part in because I thought that's what I have to do to survive," Gamal said.
"One of the earliest experiences was when I was at Hendon at the training school and I was in my room doing some studying and some guys knocked on the door laughing and joking and said 'you're the wrong colour to be in this job!'.
"They grabbed shoe whitener and they painted my face white.
"I look at that picture now and I feel sorry for the guy in white with the white face because that's what I allowed to happen to me," he explained.
Mr Turawa retired as an officer from the Met Police in 2018 and believes there are "a lot of good cops" but more should speak out against racist officers.
"Not every officer is racist but the ones that don't say anything allow the racists to exist," he said.
"There are a lot of good cops but the good cops need to start standing up now and saying 'no, this is not happening on my watch', Gamal added.
On Monday, the Metropolitan Police Federation said it had "no faith" in London Mayor Sadiq Khan after the "very public ousting" of Dame Cressida Dick as commissioner.
The body representing more than 31,000 rank-and-file police officers claimed comments made by Mr Khan have "undermined the professional, dedicated and incredibly difficult work of tens of thousands of hard-working and brave police officers from across the capital".
Gamal Turawa urged to Met Police Federation to re-examine their comments and ask themselves "what side of history do you want to be on?"
He added: "We are at a turning point and rather than looking for someone to blame let's look for ways to change things and make things better."
Gamal said the colour of the new Met Police Commissioner did not matter and they would be judged on their plan to tackle discrimination.
The Met Police said there was no place for racism, homophobia or misogyny within the force. A big recruitment drive is also underway for hundreds of new officers to improve diversity.