Tia and Tamera Mowry were rejected from a magazine cover because of their race.
The former 'Sister, Sister' stars were keen to feature in a publication aimed towards teenagers when they were younger, but were told they wouldn't be popular cover stars.
And Tia admitted she will always regret not speaking out at the time about the fact that "wasn't right".
She said: "My sister and I wanted to be on the cover of this very popular [teenage] magazine at the time.
"We were told that we couldn't be on the cover of the magazine because we were Black and we would not sell.
"I will never forget that. I will never forget where I was.
"I wish I would have spoken up. I wish I would have said something then. I wish I would have had the courage to speak out and say that wasn't right."
The twins' mother, Darlene, taught the pair what it meant to be a "strong, confident, beautiful Black woman."
Tia added on ET's 'Unfiltered': "She used to always tell us, 'Do not let this business define who you are. Don't let something like that tell you who you are, and tell you what your value is. Because it's not true.' "
And it's a message of positivity that the 42-year-old star - who has a nine-year-old son, Cree, and a two-year-old daughter, Cairo, with husband Cory Hardrict - has passed on to her own children.
She added: "To this day, I'm always telling my beautiful brown-skinned girl that she is beautiful.
"I tell [my son] how handsome he is, I tell him, you know, he is smart.
"Because I know what it feels like for someone to devalue your worth, and I don't want my children to ever, ever, ever, feel that. And not have the strength, or the foundation, to not believe it. To believe that they are worthy."