This GaiaUB image of the Gaia's focal plane was selected as the image of the week on the ESA's Gaia page.
To optimise the transmission of light from the vacuum of space into the silicon of the light detectors, the silicon is covered with a very thin anti-reflective (AR) coating. The thickness chosen for that layer depends on the wavelength range which is to be observed with a particular CCD detector.
The model of the CCDs used for that purpose does not only allow to determine the amount of light that is absorbed by the CCDs as a function of wavelength, but also to compute the fraction of light reflected from its surface. Using the latter information, it is possible to compute the colour of the CCDs as a human being would see them, as a function of the thickness of the AR coating. The colour of the Gaia's eyes.
The small frame in the image shows the colour in which a human being would see a Gaia CCD as a function of thickness of the AR coating.
Credits: ESA/Gaia/Airbus DS/DPAC/IEEC-ICCUB/M.Weiler