I recently asked a physics professor to cite some observable natural phenomena whose explanation essentially requires Born's rule. He cited the sky's being blue. But I've had some trouble confirming this through online searches. Typically one finds the claim that the blue colour of the sky is caused by the scattering of sunlight off the molecules of the atmosphere. This so-called 'Rayleigh scattering' is more effective at short wavelengths (the blue end of the visible spectrum). So the light scattered down to the earth at a large angle with respect to the direction of the sun's light is predominantly in the blue end of the spectrum. Where exactly does the Born rule fit into that standard type of explanation?