who is a famous black author that does not appear black?

This could be either Alexandre Dumas, author of "The Three
Musketeers," or his son (also named Alexandre Dumas,) author of
"Camille."

"Alexandre Dumas was born July 24, 1802 in Villes-Cotterets to a
French noble father that had settled in Santo Domingo (now part of
Haiti). His paternal grandmother, Marie-Cessette, was an
Afro-Caribbean that had been a black slave in Santo Domingo. There is
no indication that Dumas ever defined himself as a black man, although
his works would later be popular among African-Americans, probably
because the tales were often stories of emancipation, and a shorter
work, Georges (1843), specifically examined the issues of race and
colonialism."

http://www.nairohe.com/montecristo/tale.html

"Dumas did not generally define himself as a black man, and there is
not much evidence that he encountered overt racism during his life."

http://www.kirjasto.sci.fi/adumas1.htm

Here is a photo of Dumas père:

http://www.clevelandart.org/images/museum/collect/photo/nadar1.jpg

And a portrait of Dumas fils:

http://www.senat.fr/evenement/archives/Adumas.jpg

Another possibility is Patricia Nell Warren, author of "The Front
Runner":

"I could pass for "white" -- fair skin, blue-grey eyes, brown hair.
But my native American blood is visible to anybody who looks hard. One
many-times-greatgrandmother of mine, Keziah, no last name recorded,
who married a German Quaker in the early 1800s, was evidently an
escaped slave. Yet nothing in my outward appearance hints at Keziah's
presence in my family tree."

http://www.spectacle.org/996/warren.html

A photo of Patricia Nell Warren:

http://wildcatintl.com/images/patnell.jpg

Or Toi Derricotte, author of "The Black Notebooks":

"These journals were kept by African-American poet Toi Derricotte, who
can 'pass' for white, when she lived in an affluent white suburb of
New York with her much darker-skinned husband."

http://www.powells.com/cgi-bin/biblio?inkey=62-0393319016-0

A photo of Toi Derricotte:

http://courses.lib.odu.edu/litfest/11th/derricotte.jpg

And Pushkin, too, of course.

Your question is in the present tense, so maybe you're looking for
someone who is still alive. If so, my suggestions won't be helpful.
But Anatole Broyard was a well-known critic (mid-late 20th Century)
who decided early in his career to "pass" as a white man, and he
became a very prestigious critic for the New York Times. I believe
that late in his life he wrote about being black, stunning most people
who knew him or knew of him.

Nella Larsen, a Harlem renaissance writer, wrote a well-known novel
called "Passing," but unfortunately I can't remember off the top of my
head if she herself "passed" as white. Since I'm not sure you're
looking for dead writers, I won't bother checking, but it shouldn't be
hard to find out on the web if you're interested.