There is no reason if, (and I say If as I dont believe it was ever used) a kid covered mic would be whiter in colour as with any leather it comes naturally coloured and can be articicially coloured. But good kid is as thin as a few layers of silk, hence why I doubt it was used.
As for chamois, as it is a natural material you would be hard pressed to find two pieces the same colour, even if cut from the same hide. A very good quality chamois that has been finished well might be better as it would be bleached or coloured to an extent, but that would be mostly used in fashion (even of the period) so would be finished to a high quality for that reason.
Chamois is very soft and light yellow in colour when new but dries and dulls with age and wear. In the same way that repro officers cap badges (for example) often look wrong because the bullion is too bright, you are looking at them from a collectors point of view, in that you are more used to seeing a badge that is 70 years old with dulled bullion that has oxidised.
A new mic, covered with chamois 70 years ago would be very light in colour and soft to the touch, which would be exactly the same with a recovered example made today (such as my recovered, original Type 19 mic). But its looks unnatural because you are more used to seeing preserved examples that have 70 years of ageing, drying and wear on them. My chamois was a £3.00 cleaning cloth from Halfords and looks fine. Its been done a couple of years now and has been handled so looks less than new.