I am 100% with Tim on this colour debate.
Don't be silly! There is a huge range of choices for colour filter arrays and they come in varying densities too.
This is true.
On top of that, there is also manufacturing variation in the spectral responses of CFAs, certainly within a sensor (pixel to pixel), and probably also between sensor batches. What you see in the datasheet for a sensor is only indicative. Shashin, look up the KAF-40000 datasheet for your 645D's sensor. The title over the spectral response curve says "KAF-40000
Average QE", while the next plot is captioned "
Typical GR - GB QE Difference" [my underlining].
Then look up the KAF-31600 datasheet (same sensor size and microlensing, just slightly bigger pixels) and you'll see a noticeably different set of curves.
You can't apply a profile that corrects one and not the other.
Exactly, and this is the nub of the matter. Shashin talked about getting Photoshop to correct the disputed metamerism. But a pixel's colour is just a set of 3 numbers for R,G,B. If a fern pixel has an R,G,B of 30,94,12 and a moss pixel has an R,G,B of 30,94,12 also, how can you ask Photoshop to treat them differently from each other?!
Once the image capture has taken place, you can play with and rescale the ratios between the 3 R/G/B numbers in post processing, and this gives the illusion of infinite colour flexibility, or the illusion of perfect colour accuracy if you've taken a lot of trouble to profile things. But no playing or profiling can drive equal valued pixels away from each other. You can make them dance all over the gamut diagram, but they are always moving as a unit.
If you want a simple test whether cameras sensors can cause metameric shifts, try taking a photograph of a GATF/RHEM light indicator under a light source where the colours all look the same for your eye. I guarantee the colours will look different to the camera sensor - that is metameric failure.
Or do this simple test: shoot a street or garden in daylight, and again at night under low pressure sodium street lighting. All the varieties of object and foliage colour in the day shot collapse to essentially the same, almost monochromatic colour in the night shot. Ah, you say, but that's a metamerism problem due to the light sources, not the camera sensor. But wait, there's more! Do the test twice - use both a Kodak sensored MFD unit and a Dalsa sensored one, or if you can't manage that, use both a Kodak sensored MFD unit and a DSLR. Equalise their colours to each other as best you can in the daylight shots - and then apply those settings/profiles to the night shots. And be prepared for the shock of vastly different colours! Kodak sensors, at least the older ones like the KAF-18802 and KAF-2002CE that I have used in my MFDB and DSLR, record the yellow-orange (589 nm) emission of traditional low pressure sodium lights as yellow-green! [See my examples below]. That is an undeniable example of getting the colour "wrong". It can't be profiled away, nor fixed with a white balance correction; if you attempt to do so then you throw off the colours of anything in the photo which was not merely reflecting the sodium lights...such as car headlights and the objects they illuminated, or the Moon, or the remnants of a twilight sky.
Moon, Venus, and a few stars. 200/2.8 APO and Kodak DCS645M on a Mamiya 645AFD, 4 second exposure. I took this from just outside my house. The foreground bushes, which had bare brownish-gray branches in daylight, were very close to a sodium streetlight (it was just over my right shoulder). They should therefore look yellow-orange, but instead they are a stark yellowish green. The Moon, slightly warmed up by the hazy twilight, shows that there was no major white balance problem elsewhere in the scene. If I were to click white balance off the moon to make it more neutral grey, it would "cool" the colours of everything else in the scene, which would only drive the bushes further from the warm orange they should be.
So I have seen clear cases where Kodak sensors deliver weird colour because of where the CFA response curves rise, fall and cross each other in wavelength space. The green filter is either not falling quickly enough at 589nm, or the red filter is too slow in its rise into the orange region, or both.
If this is a pronounced issue in monochromatic light, it will be a more subtle - but no less real - issue in daylight.
Now, while this greenish colour is clearly "wrong", I sometimes prefer it to the "right" orangey colour, because green trees and bushes are more natural than orange ones! The yellow-green is not so lurid when the objects are not as close to the steetlight(s). See the next example.
Second example - Orion, Jupiter and the crescent Moon. A pano made with the same camera and back, 45/2.8 S lens, 30 second exposures. Where a high-pressure sodium security floodlight caught the treetops, they are the correct orange-yellow colour (because high-pressure lights are broadband, not monochromatic). But look under the treetops at the rest of the trees, especially over on the right - there's that yellow-green again! Those parts of the trees are dimly illuminated by low-pressure sodium streetlights. It's the monochromatic nature of this light that is so unforgiving: if your CFA filtration bandpass is slightly off, then there's no fixing the colour.
To the eye, both types of light were yellowish, but to the camera, reflecting off the same material, they record as completely different colours. [I guess this is like the inverse of metamerism - is there a name for that?]
Ray