The story takes place in Chromatacia, an alternative version of the United Kingdom wherein social class is determined by one's ability to perceive colour.

Details reveal that East Carmine is located in Wales (the A470 road is mentioned), and the description of the town close to the lower of a series of five dams suggests it is Rhayader, at the foot of the Elan Valley.

Protagonist Eddie Russett is a 'Red' sent to the outer-fringe town of East Carmine to conduct a chair census, which he speculates is punishment for a practical joke played on the son of a prefect.

Specifically he learns that misfits, supposedly sent to Emerald City to be brainwashed, are taken to the deserted town of High Saffron where they are killed by looking at a building whose colour is poisonous.

[2] In February 2021 Jasper Fforde announced on twitter @jasperfforde that "In March I start work on Shades of Grey II, which should be published 2023.

[4] The final book in the trilogy, tentatively titled Shades of Grey III: Blue Yonder, is planned to be released in 2027.