Writer's Digest magazine features an article by Tiffany Luckey on DORK DIARIES author Rachel Renee Russell. It's a great article.
When asked how she feels about authors writing about cultures other than their own, Ms. Russell said this:
"Authors of any race and gender should write - number one - what their heart and brain are leading them to write, and - number two - what they're passionate about."
"Authors of any race should be able to write other races. We see [white] authors writing people of color [all the time], so, to be fair, people of color should be able to write other races [as well]."
(Ms. Russell is African American, and her DORK DIARIES protagonist Nicki Maxwell is white.)
She also gave this bit of general advice:
"Write what you are comfortable with, write what you're interested in and what makes you happy."