To remove color from; to make colorless (British English spelling with -ise suffix).
From de- + colour (British spelling) + -ise (British verb-forming suffix from French -iser). The -ise ending is standard British formation for verbs alongside -ize in American English.
British scientists actually write 'decolourise' while American scientists write 'decolorize'—but here's the fun part: both spellings are 100% correct in their respective countries, showing how English adapted to two different but equally valid spelling systems!
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