What causes the crema in my latte to appear so charred? My latest attempt at creating latte art (admittedly theres still room for improvement).  

My question is, what is causing the crema around the milk to have such a charred look to it?  It isn't immediately noticeable after adding the milk but within a minute after it starts developing that charred appearance.
Hard to diagnose just on the back of a photo, but if I had to guess, I'd say the milk is not "sunk" properly (i.e. the consistency of your espresso is different to that of the milk). This would also explain why the base of the rosetta is a bit "murky". That took me a while to figure out, but I had the same issue (check this out, then compare to this). So in practical terms, avoid wiggling the pitcher before a white "dot" appears on the surface. Only once the white dot appears on the surface and the stream of milk coming from the pitcher has pushed it further into the cup, should you start rocking the pitcher left to right (good examplehere albeit a different pattern). Hope this helps!