You have a yellow lamp in your spaceship. Now you accelerate your spaceship significantly. Then you stop accelerating. Does the lamp still have the same color? I would think it should, but I reckon differently as follows: Consider the situation from an outside observers point of view, resting in the frame of before the spaceship was accelerated. a) The light undergoes a Doppler shift when emitted from the lamp, but exactly the opposite Doppler shift applies in the retina of the moving observer, so this would not change the color. b) But, compared to the rest frame, time on the spaceship runs slower, meaning the moving observer's time runs slower by the Lorentz factor, allowing more light waves to hit his retina within his standard time interval, hence a higher frequency. Incidentally, the frequency is higher by the Lorentz factor, which does look right. To get rid of any strange effects going on in the light emitting process of the lamp, we could assume to have captured a beam of light in a mirrored box before the acceleration phase, letting it out afterwards. The arguments (a) and (b) still apply and the beam of light should now be blue shifted for the moving observer. Is it blue shifted or not ?