I've just added a new sky2 light using the Hosek and Wilkie model. All the code is mine, but the model and the data is theirs. Please test it and let me know what you think of it. EDIT: the current code doesn't yet allow to specify the earth albedo, but that will be a natural extension if you like it.
It's indeed looking wrong. I have also found some situations where I get this greenish look, or a black zenith area. I have yet to figure out what's going on since it is otherwise mostly working. Maybe it's due to the different interpolation I'm doing or a wrong angle computation somewhere. I'll try to make some automatic testing and comparison with the original code.