I don't think you can make a general rule for "multi" tone.
I use "multi" vs 2 tone term, because lots of 71-73 are duo tone. Black scoops hood with body color aren't that rare...
It always comes down to the way its done. How it suits the shapes, the color harmony once the combo interacts with light
and of course the quality of execution.
As an ex art director, I can tell you that picking the right set of colors is a discipline on itself and very often why the result fails to please the eye.
Tools like this one for instance, even if designed for screens, are a great way to generate combos that doesn't make your eye bleed even using colours you would not want to use looking at the one colour alone.
https://color.adobe.com/create/color-wheel/
Using classic and wrongly thought safe combos, like red/grey/white, blue/black/white/grey etc.. aren't gonna work perse even if used countless times.
I've seen enuff classic "safe" combos fail once applied just because no to little attention is brought to their relationship on the shape of the car.
It's all the red you that you pick, the additional metallic particules size, the percentage of surface visible to the eye, how near the domiment color is to the other...
On my part I welcome anything, any colours if well combined.
We'll soon see how Angelo feels about that! (no pressure)
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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