One of my favourite models from the "straw" box era is the Y24 Bugatti. "Made in England" production models were a stately black, with varying yellow panels, but many colours were used in the development process. First run bodies were in metallic blue, and the bonnet was too short.
Later, when the box was being designed, red/yellow/silver was trialed. Allegedly only 48 were made in this colour combination. A number I would dispute. Probably nearer a couple of hundred judging by the amount I've seen over the years.
Many different "colour trials" exist, and I can show some more if any interest.