Very nice picture! Let's see if Comet ISON ever turns out to be that bright. For a comet that was predicted to become perhaps as bright as the full Moon, ISON has been a no-show so far.
For me as a color commentator, the picture is interesting. The tails of comets are generally white, if they are dust tails, and blue, if they are ion tails. Cometary comas are almost always green. The tail of Comet McNaught seems very faintly bluish, but washed out. The coma appears to be quite yellow!
Perhaps the comet was a "dusk object", so that it was seen low in the sky and therefore quite reddened.
The colors of the three galaxies in today's APOD are also interesting. The bluest-looking object is the Small Magellanic Cloud. I think that is correct. The U-B and B-V indexes of the SMC are -0.200 and 0.450, respectively. Both values are blue. Also the far infrared magnitude of the SMC is comparatively faint, 0.7 magnitudes fainter than the B magnitude, which suggests low levels of dust in this galaxy. The SMC is made up of generally metal-poor and therefore somewhat bluish stars, and it lacks any sort of concentration of old yellow stars. It does have star formation and young blue stars.
My software contains no information on the Large Magellanic Cloud as a galaxy.
Nevertheless, unlike the Small Cloud, the Large Cloud has a clear inner structure and an obvious organization of its stellar populations. The LMC has a bar, which is older and yellower than the rest of the galaxy. AURA/NOAO/NSF has taken a picture of the LMC where the bar of the galaxy looks unrealistically yellow
. But other pictures too
show that the bar of the LMC is yellower, or at least less blue, than the rest of the galaxy.
The LMC is seen to contain one intensely blue dot. What is this dot? Well, R136 of course, the huge cluster powering the Tarantula Nebula! But then where is the red light of the Tarantula? We don't see it because no Ha filter was used to produce this image. Bear in mind that the blue stars of R136 produce very much more light than the red nebula, so the filters or film used for this picture detected the stars but not the nebula. Compare with this image
, which also shows the Tarantula region as very bright and blue.
Finally there is our own galaxy. While the Milky Way has a respectable rate of star formation, it also has a large population of old yellow stars and a thick central dust lane. All in all, it is clear that the overall color of the Milky Way is much yellower than the color of the Magellanic Clouds.