It’s the way financing these days works on brand new cars.

The buyer is paying off the difference between the price at the time of sale and the price at the end of finance term (plus interest on the difference)

The price at the end of the term is due to depreciation. If the buyer opts for a neutral/non-polarising color, then the depreciation is lesser than compared to choosing a different color. This is because it is assumed (mostly correctly) that it will be relatively easier to sell a grey/black car than a bright yellow/red car.

That also results in the non-neutral coloured car costing more to finance over the term.