Those yellows on that last pic have about 5 layers not counting the primer or a wash to give it a dirty look.
I actually tried several different techniques on all the large areas just to see which worked best.
In the end they pretty much all came out pretty close to the same thing.
For me I liked this process...
1. Prime black
2. Iyanden Darksun foundation
3. Skull White
4. 2 coats of Sunburst Yellow
5. detail work, i.e. chipped paint and such
6. Devlan Mud wash
The yellow was actually very brilliant after step 4 but I thought better then having a "happy sunshiney feel good" kinda yellow on my orky stuff.