Where they see in black, white and grey
23 July 2017 Last updated at 11:11 BST
Belgian photographer Sanne de Wilde is fascinated by the colourblind people of the Pacific island of Pingelap.
A significant proportion of residents suffer from achromatopsy - total colourblindness.
It's thought that in 1780 the population was all but wiped out by a tsunami.
As few as 20 people survived, one of whom was the king, who was believed to have had a genetic fault that caused colour-blindness, and which was passed on to his descendants.
Sanne de Wilde's images are in a new photobook, The Island of the Colorblind.