In article ,
The Other John wrote:
On Sun, 31 Dec 2017 11:58:41 +0000, Harry Bloomfield wrote:

All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

Yes, it was shown that certain flicker rates caused the brain to 'see'
colour. An OXO commercial was shown and some people saw the gravy as
brown and some as purple. It didn't catch on.

Tomorrows World showed something like that in the late '60s. Sadly, the
film was American and intended to be shown at 24fps. In the UK showing it
25fps gave completely different results to the script

--
from KT24 in Surrey, England