"You know, he's like, 'We don't have a holiday of our own. We celebrate everybody else's accomplishments, but important moments in our history, we don't,'" Anderson explained to ABC News.
Dre's idea is to replace the Columbus Day holiday with a Juneteenth holiday -- celebrating the announcement of the abolition of slavery in Texas on June 19, 1865, and the emancipation of slaves after the Civil War.
"Juneteenth is a huge deal for him because it is the day that abolished slavery. And he feels that we need to celebrate that," Anderson said. "Here we are celebrating Columbus Day, a man who didn't even set foot in North America, and 'discovered' America while he was lost at sea. But Juneteenth isn't acknowledged at all. So, he's on a campaign."
Turns out that campaign involves joining with guest star and R&B singer Aloe Blacc to write a 'Hamilton'-like Juneteenth musical.
"We get our 'Hamilton' on, man," Anderson said. "We have two huge musical numbers that are flashbacks to us working on a plantation. So it'll be interesting to see how audiences respond to that."
"We learned it really fast. And I felt so proud of our cast," she told ABC News. "I felt like ... 'We're going to take this on the road kids!' These two numbers are going out for regional theater. Or Broadway. We'll take Broadway."
"Black-ish" season four premieres Tuesday night at 9 p.m. ET on ABC.