Tan ruined when switching sides (5)
I believe the answer is:
brown
'tan' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for brown that I've seen before include "Former PM" , "cook to a rich colour?" , "It is used for wrapping" , "Kind of sweetener" , "Labour PM, b. 1951" .)