Nice, clean paintjob. Yellow is aways hard to do (in my experience) but you did a good job of it. A bigger pic might make commenting a bit easier, too.....
I really liked the look of the old Ulthwe so I just changed it a bit to more personalize my army... Instead of going primarily black with the tanish look I did the opposite. It is Scortched brown, Rotten flesh, then highlighted with bleached bone to white.
I am very happy with this fella.
And yes... blending and working with this yellowish combination takes ALOT OF LAYERS and time. Especially when working with such a huge surface area!