The use of the color distance measure turns out to be important in spam filtering because of the 'Camouflage' trick used by some spammers where similar, but not identical colors are used to mask chunks of 'good' text inserted to try to fool spam filters.
Camouflage (GWI!Camouflage!HTML)
What: Like Invisible Ink, but instead of using identical colors (e.g. white on white) use very similar colors.
Date added: June 2, 2003
Example from the wild:
The colors 1133333, 123939, and 423939 are chosen to be very similar without being the same)
From http://www.jgc.org/tsc/
Camouflage (GWI!Camouflage!HTML) What: Like Invisible Ink, but instead of using identical colors (e.g. white on white) use very similar colors. Date added: June 2, 2003 Example from the wild: The colors 1133333, 123939, and 423939 are chosen to be very similar without being the same)
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