Update: Markk commented below that the picture above might actually be the Lumia 900. The image does suggest this could be the first leaked picture of the 900; look at the positioning of the buttons, they are more spaced out and there’s less empty space under them unlike the Lumia 800. The camera button is also positioned a little higher than on the 800. We could definitely be looking at the Lumia 900 here.
It is very usual for Nokia to silently release color variants of a smartphone months after it was first introduced. History might repeat itself with the Nokia Lumia 800. Nokia recently showcased for Microsoft France the Lumia 800 in alternative colors. Nokia said they were considering adding colors to the present lineup, but they had not decided what tones in specific–white and yellow were displayed in the presentation they were giving though. The purpose behind these new variants is revitalizing sales after a few months on the market.
I think that a yellow or white Lumia 800 would be something to show off; I checked out the white N9 over at Nokia World, and I have to admit, it looks better than my blue N9.