It is black in the daytime, but those sodium street lights make everything look orange at night.

The black oil is in its original form. The reddish lumps are what they call "chocolate mousse", oil that contains emulsified water, what in some contexts is called an "invert emulsion".  Why that makes it change colour (it doesn't always come out red, depending on the oil type) is something that there is a lot of agrument about.

My impression is that it is partly because light can penetrate more deeply into the water-wet oil, and pick up colours that otherwise would be masked by the black bulk. Also, in contact with the water, some components, such as decomposed porphyrin residues from fossil chlorophyll in the oil, would show colours that they would not show when suspended in the oil. 

I have actually known residues to show reddish colours from iron oxides in oily residues, but I doubt that this oil would contain as much iron as it would take to make it as red as the pictures show. My bet is decomposed porphyrins.

NB! I said bet, not diagnosis!

Interestingly, I was also thinking the same question few days back and with almightly google, found this link with the clear answer:

http://www.slate.com/id/2253636

From the above link : "Bonus Explainer: Why does the oil slick appear to be orange instead of black? Because the emulsion of oil in water consists of particles of many sizes, separated by water molecules. The way these particles scatter light (and produce color) depends on their size, and their size can change over time as they clump together or separate. "