Nothing special really. For the rear wheel guards, I based the whole model in Averland Sunset (since the orange is Blazing Orange which has poor coverage over black) then painted around 6 layers to blend from pure Averland Sunset gradually mixing in more Blazing Orange to get pure orange at the rear of the wheel guard.
The only slightly tricky thing was I used feathering with a fine detail brush to blend the layers together rather than giving sudden transitions from one layer to the next, something which I haven't really done much of in the past. Normally I'd use heavily watered down paints to make each layer semi-transparent and blend it, or do a bit of wet blending, however I find those techniques are good for small detailed areas, but they turn out messy for large flat areas like this. The other advantage compared to using transparent colours, with transparent colours you have to repaint the entire area (minus the small area that's the previous colour) with each layer, but with feathering you get away with just painting the few millimeters that actually need to be that tone before moving to the next tone, makes the whole process a lot quicker (at least for a model like this).
The flames I did in a similar fashion, again I painted the entire area Averland Sunset, painted the outline of the flames with Blazing Orange, then used feathering to blend the Averland Sunset into the Blazing Orange. I then painted the black last of all, carefully going around the flames with a fine detail brush before getting a big thick brush to finish it off.
The Averland Sunset is good because it only takes 2 or 3 coats over black to get a solid colour. It's not a super bright yellow, though it looks ok for this purpose since it looks bright next to the black and orange.