I'd say at least that with our limited chroma resolution, we generally may not remark that an image has a chroma resolution a bit behind its luminance resolution?
While true, things aren't as black and white (pun intended).
Restricted to the Fovea centralis
, which is occupied mostly with cones (for colorvision), human visual color resolution peaks when enough light is available. Color information by itself usually has a low spatial frequency contribution to our vision and in scenes of natural objects (it's more of a warning signal at a distance, because e.g. Red may be warm/hot/blood). That is easily demonstrated in a Lab (or HSB or HSL) respresentation of an average image, there is little resolution to be seen.
However, the human visual system (HVS) depends heavily on pattern detection (to avoid information overload) for detail discrimination, and therefore luminosity as a means to convey the important (edge detail) message is rated higher in our brain. So counting cones and/or rods alone is not telling the whole story. Contrast, or MTF, is very important for our detail resolving abilities.
The HVS, which involves the brain, therefore has a variable resolution depending on average scene brightness and luminosity contrast. The brilliant weighting of a Bayer CFA is a very good (although not perfect) instrument to allow the most relevant
information to be recorded. The fact that the cones of our eyes are more randomly distributed complicates a direct comparison with an aliasing prone ordered sampling method.
Nevertheless, as also Emil has demonstrated above, it is possible to achieve a visually
very good/convincing reconstruction of the actual scene with only a faction of the data (which saves a lot of storage and speeds up the storade (frames/second) and transfer of data). In fact, when one analyses the R, G, and B, MTF resolution of an image (e.g. in Imatest) with adequate luminance contrast, the RGB resolutions of a Bayer CFA image are virtually identical to the luminance resolution. Only in the worst case scenario of chroma resolution in the absence of most luminosity contrast info will there be a benefit for full RGB resolution/sampling. When enlarging the resulting image, there is an obvious, although limited, benefit to having as much accurate (also RGB) data available.