From dis- + colour
discolour (third-person singular simple present discolours, present participle discolouring, simple past and past participle discoloured)
- British and Canadian standard spelling of discolor.
2021 January 13, Christian Wolmar, “Read all about London's Cathedrals of Steam”, in RAIL, issue 922, page 63:
Instead, the grime of the steam years which still discoloured many of the best architectural features Betjeman loved has been cleared away, and several of the stations have benefited from major refurbishments which have greatly improved them.