I have a 'thought experiment' which I'd like to ask about.
I was thinking what speed I would have to drive towards a crossing to see a red light as a green light - pretty easy, using the doppler effect for electromagnetic waves. I'd have to be driving around $1/4\times c$. Now I started wondering... how would I see something purple?
Like what if there would be a purple (smallest visible wavelength) ball next to the street, the wavelength would shift out of the visible light spectrum for me so would I just NOT see the ball? Or does it also radiate other wavelengths which would shift into the visible light spectrum?
Assuming it doesn't, would I just not see the ball?