No one could see the color blue until modern times (businessinsider.com)

Gladstone wasn't aware that the Greeks and other ancient peoples used brightly coloured paints on their statues and buildings.

Because articles like the linked one keep coming up, I've just submitted on HN an article from the British museum about the extensive findings of "Egyptian blue" on the Parthenon:

https://news.ycombinator.com/item?id=9972478

This shows that Lapis lazuli was available throughout the Mediterranean, not just Egypt.

Cobalt was used to colour glass during the Bronze age:

https://en.wikipedia.org/wiki/Uluburun_shipwreck

The Mycenaeans used blue glass for necklace pendants:

http://www.cmog.org/artwork/necklace-glass-pendants-and-faie...

The colour blue has also been found in mosaics and paintings unearthed at Pompeii:

http://www.pompeionline.net/pompeii/painting.htm

When examining the existing ancient literature to extrapolate on colour perception, it's important to remember that only a minuscule fraction of ancient literature survives to this day.

And people couldn't communicate before email.

This article claims that some Himba subjects were entirely unable to discriminate blue from green, but this alleged experimental finding is a myth owing to irresponsible BBC producers. See these Language Log posts:

http://languagelog.ldc.upenn.edu/nll/?p=17970

http://languagelog.ldc.upenn.edu/nll/?p=18237