On Wed, 07 Apr 2021 23:15:00 +0100, Graham Harrison
wrote:

snip
There are too many colours on the map already, enough to make it
impossible to distinguish between them for some of us.

Too many designers fail to appreciate the issues of colour blindness.
It's not just the London Underground Diagram, web pages, print
advertising; almost anything that uses colour. I sometimes think
patterns might be better but I find myself wondering if they might
cause other problems (epilepsy?).

When I was tested for colour blindness there was some interesting
literature I was provided with which suggested that the spectacles
that get prescribed for colour blindness have been shown to help some
dyslexics. I don't know, just reporting what was claimed. But one
thing a dyslexic child was claimed to have said stuck with me "the
letters in the words dance across the page". It made me realise
there's an awful lot we don't know about ourselves.

That dyslexic child is not alone. That effect is one of the reasons
you see some people reading while moving a rule under each line or
moving their finger along the text (other than when that is done to
keep your place while reading out to and intermittently looking toward
an audience).