reply to post by nablator
I don't think there's a way to explain it conclusively (i would be a liar if id claim the contrary

)
but of course, there are a many possible explanations:
from the atmospheric factor to ISO noise: 4 seconds are an extremely long exposure time, in four seconds many things may happen
for instance, take a look at this photo by ignorant_ape, showing an aircraft, and you can notice that the lights turn their color
you can also try by yourself, setting the camera close to the settings of the photo of the op, and taking some shots of some blinking objects: i guess
that in some attempts you could get some variation in the colors:
the only problem, though, is that the variation seems to affect only that specific light, as if the noise or whatever it is, affects just a part of
the spectrum, in this case the one closer to green:
but who knows?
It looks an airplane to me