Overall I like the yellow you've achieved and would love a step by step guide on how you've done it. That being said it looks a bit to clean for Orks, maybe try a wash or two and see how that turns out. Also you might want to try and add another light or two to get the lower sections of the models. Right now its to dark to make out much below gob level.
Coming soon! Got half of a tutorial sorted just need to put time aside to finish the painting.
As to lighting still am trying to work out the best ways to get these photos working, the new ones are better but still more work is needed.