Progress! Have taught myself how to paint yellows. Here's a step by step of how it went:

This is attempts 1, 2 and 3.
Starting on the front mudguard, undercoated white, basecoated golden yellow and then drybrushed sunburst followed by badmoon. Complete disaster. At this stage I asked for help.
One of my store staff suggested Tausept Ochre drybrushed Iyanden Darksun, so that's on the back driverside mudguard. Nice, but sandy rather than yellow.
He then suggested Iyanden darksun mixed with golden yellow, and highlighting up from there. Passengerside mudguard. Didn't really work.
I realised I was going to have to test this out on a different miniature. I wasn't willing to spend much, so I bought a cheap T-80 and had my way with it. I started airbrushing as well, as it's fairly different to brush painting. As you can see, vast improvement.

I started with a white undercoat, then sprayed golden yellow. I shaded with firey orange wash. I went over again with golden yellow, and then 2 more coats with increasing amounts of skull white mixed in. This obliterated the shading, so I went over it with another wash of firey orange. It ended up a bit dark.
So I did the whole thing white again and re-did it, this time with lighter shades and washes at the end. I slightly overdid the highlight in the middle of the turret, but it was a vast improvement over the SM Bike.
Finally, I painted the head of the titan. I wanted something a bit richer, so I started with Sunburst mixed with firey orange and highlighted from there. At the end I shaded with the same mix diluted into a wash.

I'm very pleased with how it came out, and am now moving onto detailing.
