The process or action of removing color from something (British English spelling).
From decolour + -ing (gerund/present participle suffix). British English maintains the -our- root spelling even in the -ing form, unlike some other British words.
British and American speakers use '-ing' forms identically—'decolouring' and 'decoloring' are just spelling variants of the same word, showing that not all British-American differences involve pronunciation, just written form!
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