It has been a long wait, but so worth it: the Rosetta OSIRIS science camera team has delivered the first pile of data from the rendezvous with comet 67P to ESA's Planetary Science Archive.
Dumb question. Are those pictures in color but it happens to be a grey object or did they use a black and white camera? Tagging you francopoli because this stuff is your jam.
The very short answer is that this object is mostly black and grey and white. From last year this is about what you would see with your eyes. These objects are about as dark as fresh asphalt, reflecting less than 10% of the light that hits them. Much longer answer is that the camera is monochrome. The CCD is a very sensitive light collector that they use filters to get the "colors" you see in the images. Every wavelength of light tells you something about the object. The article linked above gives much more info on how the cameras work.
