eli5: Why does blue shift in astronomy equal an approaching object and blue color in doppler ultrasound equal movement away?

Question

I’m in a class that is discussing the operation of diagnostic ultrasound and I was confused by the colorization.

In: Physics

Answer 1

The operator has control over the color scale on an ultrasound machine and can invert as needed. This is done mostly due to convention and for consistency – arteries are displayed as red, veins as blue.