The secret to painting yellow is to get an even coat, on each layer, when layering up to white. The first picture is not good enough to escape notice, but the second on is. In the video I dont start in the beginning, in fact I start between the codex grey and fortress grey colors. This technique can only be used on simple designs, but that doesnt mean you can not complicate the design later.
On a dark color vehicle start with:
1) clean the surface of any oils from your hands
2) using the technique demonstrated in the video layer up the following colors
-golden yellow (optional if previous layers done well enough)
-bad moon yellow (brightest yellow possible)