"I change my hair color all the time and I hadn't done it in a few years," added Richie, 28, who lopped a few inches off her blonde hair earlier this year. "With the babies, I just really hadn't had time."
The reality star (who will produce her own scripted sitcom for ABC) welcomed son Sparrow this past September, and daughter Harlow -- who she says "loves being a big sister" -- in 2008.
"I'm so used to having that change all the time, and I hadn't done it in about two years, so I was just ready and sick of being blonde!" she continued. "I was ready for a change!"
Richie also opened up about how she'll spend the holidays with her beau Joel Madden.
"I don't have a lot of traditions," she said. "I have gotten a new Christmas ornament every year so I will probably do that. I'm a big eggnog drinker. Not the kind with alcohol in it, but the regular kind. I thought that everyone drinks eggnog, but as I'm getting older, I'm learning that people actually think it's really gross, but I love it, so I will definitely have some eggnog!"