A good start. But I've got some suggestions that will bring these models up leaps and bounds. First off though, the yellow itself is very well done, as I said, particularly on the airbrushed model. But there are some things you need to do to bring their level up a notch.
First off, tidy up the fist on his knee. Bring the fingers in closer, as at the moment it doesn't really resemble the IF logo too much. Work slowly and it will look much nicer.
Also there a few places that need touch ups (soft armour in wrist joint is still yellow for example
Secondly, regarding the battle damage (as i assume that is what the effect on the rear of the leg is) I think you should either spread the damage across the whole model, or not do any, because at the moment it doesn't really look "right" to me.
Next, I think you definatley need to choose a company to do, so that you can paint the shoulder trims a different colour. At the moment there is a little too much yellow on the top half of the model, painting the trims a diferent colour would help break apart the one colour look.
Lastly, paint the rims of your bases, this is a small thing that makes the world of difference. just giving them two coats of bestial brown will make the model look much more finished.
As i said, this is an exceptionally good start and my hat goes off to you for choosing such a difficult colour (I still wish I had the balls to make a proper go off yellow)
Once you've done a few things to just tidy it up and get a little more detail in there, you will have a really great looking model
hope this helps