Very interesting topic, nice find and thank you for sharing.
As far as the Net is concerned at least for my quick search the oldest Indigo dyed cloth ever found is from Peru so predating the oldest Egyptian
To see if there was a shift in our genetic make up would require extensive samples of intact ancient DNA which we probably don't have enough of.
In the bible Sapphire and other blue gem's colors may be used in place of Blue and of course the ancient Celt's whom lived in a warrior cast system
of tribal people's especially among the Britain's would paint themselves in Blue Woad a dye with antiseptic property's which could also help to
prevent infections in battle - a lot more intelligent than they were claimed to be those naked crazy Celtic warrior's.
I suspect if you do a search into ancient history the reference to Like Sapphire or like Lapis Lazuli are probably quite common so you may want to
substitute that for the word Blue which may have been a later written word used to distinguise these similar color's we today simply refer to as
Certainly if people could not see the color then we would have to ask why they seemed to value gem's of that color and why Lapis Lazuli mostly mined
in the Hindu Kush region's now known as Afghanistan was so prized that it was found as far away as Egypt and even ancient Britain from as long ago as
the neolithic period.
Of course there ARE color's to which we ARE blind, ultra violet for example.
And of course it is likely that as in the case of many that are supposedly Color blind - except those few whom suffer total color blindness whom see
the world as a monochrome that most of the rest of us with slight color blindness see it more in a phase shifted way so that our personal spectrum
would look a tiny bit different to your's since we still see color's just some are harder to distinguish.
For example the color test card when I went to join the Navy and found out that I was color blind was to me a trident with three upward pointing
spikes but to you it would appear as a 4.
Just maybe our eye's are evolving to see color more than our ancestor's.
There has been a whole history of Mandela type affects and reality shift's long before modern people claim to have experienced them, perhaps this
could mean our ancestors were actually living in a different reality to us?.
More likely they simply took the color for granted and used Sapphire and Lapis Lazuli comparison's to describe it,
"My fair Maiden with Eye's like Lapis Lazuli and Hair like Fine Wrought Gold" for example.