Showrunner:
"Y: THE LAST MAN is about gender, about how oppressive systems inform identity. We had a gender diverse team of brilliant artists, led by women at almost every corner of our production. Producers, writers, directors, cinematographers, production design, costume design, stunt coordination, and more. It is the most collaborative, creatively fulfilling, and beautiful thing I have ever been a part of. We don't want it to end."
There are tons of quotes from the books that the main cast is white + see Jordan's casting:
Rand: a young Ben Affleck
Mat: James Garner at age 21
Perrin: a young Val Kilmer
Egwene: Audrey Hepburn at age 18
Nynaeve: a young Jacqueline Bisset
Aviendha: a young Sophia Loren
Elayne: Nicole Kidman at age 18
Min: Isabella Rossellini
Moiraine: Hedy Lamarr
Lan: Liam Neeson in one of his craggier roles
Birgitte: Lucy Lawless of Xena
Faile: Cher at age 19
Thom: Patrick Stewart with hair
Verin: a young Margaret Rutherford
Siuan (after stilling): Renee Zellweger (before appearance change)
Gareth Bryne: a combination Charlton Heston and John Wayne
Morgase: Michelle Pfeiffer
Berelain: Isabelle Adjani
Padan Fain: Alan Rickman
Lanfear: a younger Catherine Deneuve
Shill.