I didn't want to click on "other" for all of them so let the li'l Unicorn figure it out. In my order of oldest to youngest.
Rarity: I think of her as Hawaiin American with light brown skin and eyes and beautiful blonde hair.
Applejack: I think she's Texan with her hair and eyes from the show and slightly tanned skin.
Twilight: Mainly White but part Asian with big green eyes and straight brown hair.
Rainbow Dash: Part Spanish, hearing her rage at someone in Spanish would be great with her red hair and brown eyes.
Fluttershy: Brown, she's kinda tiny with dyed hair and eyes like Twilight's,
Pinkie Pie: She's white and kinda plump with a little potbelly and dyed hair and big blue eyes.
Spike: A monkey, I'm not being racist, an actual monkey.