@dgar How does their color depend on their velocity? And how does their color depend on the velocity of the source of light?

@dgar Thanks. Yes, I understand the general idea about the redshift and the Doppler effect. I'm asking about how the velocity of the source of light (e.g. sun), and the velocity of the reflecting surface (e.g. roses) contribute to this effect. Are both of them important?

@ereliuer_eteer
The velocity of light is light speed. The velocity of the rose, as other commenters have suggested, needs to be very high indeed to appear blue.

@dgar No, I didn't mean the speed of light. I mean the relative velocity of the source of light (e.g. sun) to the rose and to the observer. I assume the color of the lighting is also important, not only the color of the reflective surface.

@ereliuer_eteer
…wait. You’re a theoretical physicist? Why are you asking me??! 😂

@dgar Yes, I was 21 years ago. I asked because I always thought about the red/blueshift as depending on the relative velocity of the source of light and the observer. But you introduced a reflective surface (roses), and it created a new perspective on this phenomenon, that I never thought about before, so I invited you to a discussion about it. 🙂