The pictures taken by Rosetta are BW. From [0]:
"Some light contrast enhancements have been made to emphasise certain features and to bring out features in the shadowed areas. In reality, the comet is extremely dark -– blacker than coal. The images, taken in black-and-white, are grey-scaled according to the relative brightness of the features observed, which depends on local illumination conditions, surface characteristics and composition of the given area. Some slight vignetting can also be seen in the corners of some images." So possibly Philae has a similar system.
[0] https://www.flickr.com/photos/europeanspaceagency/1573996637...
I remember having read long time ago that superposing B&W images took with those filters gives an also B&W image that our brain perceives as coloured. Does anybody know if this is correct or what's the name of that effect?
If you send three grayscale images, each one taken through a different colored filter, you can reconstruct a color image back on earth by setting the red channel, green channel, and blue channel of the image to be each one of the colored filters you used to capture the image.
This isn't a grayscale image that our brain perceives on color, but rather several grayscale images, each colored separately to combine into a color image.
I seriously doubt an actual effect exists that makes us believe black and white images are actually colored.