"Backstairs at the White House" Question

I'm currently watching the 1979 mini-series "Backstairs at the White House"...I've seen 3 of the 4 episodes.

However, I wanted to know if the characters (and real people) played by Olivia Cole and Leslie Uggams (Maggie Rogers and Lillian Rogers) were really white.
There is a picture of the real Lillian Rogers, shown with Cole and Uggams and she looks white to me.
I couldn't find anything about this online, and although it adds to the story and I'm LOVING their performances, I can't understand why their races would be changed.

They were black- but in her book ("My Thirty years Backstairs at the White House" Now out of print), Maggie (mom) says she was the first "colored" to be hired as a maid partly because she was light enough to "pass."