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Our ears are pink and fiery because there are a fair amount of blood vessels forming a network of irrigation underneath the thin skin – which lets the red color show through.
All it takes is vasodilation – an increase in the thickness of the vessels – for things to heat up. Sometimes this only occurs on a specific part of the body. Like when the ear needs more nutrients and oxygen after being held down by the phone for a long time. But vasodilation can also occur all over the body at the same time. It is, for example, an organism’s response to stressful situations.
The issue is that not all regions of your body have such thin skin or such abundant irrigation. Then, you see: if the person gets nervous, the ears end up giving away.
A curiosity is that the famous pills for erection problems also increase vasodilation. The guy who needed the Viagra thanks him, but gets red ears as a side effect.