This morning, I saw it on my phone in my darkened bedroom, and it was clearly blue and brown. Just now, I opened the Washington Post link on my 24" screen in a sunlit room, and it was clearly white and gold. I then found the link that I had seen on my phone this morning (not Washington Post, so I wanted to confirm that it just wasn't two different pictures that I was looking at), opened it up, and it was white and gold there too. Went back to my bedroom and closed the curtains, and it remained white and gold for a bit, but after I left the room (after my eyes had adjusted a bit to the darkness), it was blue and brown again. The picture on the Washington Post was also now blue and brown. Now that my eyes have adjusted to the sunlit room again (and the white Slashdot background), I switch back to the Washington Post tab, and it's white and gold again. My wife (who's now gotten fed up with following me around to look at this picture under different lighting conditions) has had pretty much the same experience as me.
So it appears to be linked to the lighting conditions that your eyes are adjusted to when seeing the image initially... even after they've adjusted to the ambient light, the brain appears to stick to the image it created initially.