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Colour contrast standard

for

From: Mike Osborne - AccEase
Date: Oct 16, 2007 1:20PM

As they say - the great thing about standards is that there are so many to
choose from.

When it comes to colour contrast there appear to be two:
* W3C - colour contrast 500, brightness 125
* HP - colour contrast 400, brightness 125

Are these numbers arbitrary or is one right and the other wrong? Is 500 too
much or is 400 inadequate?

Does anyone have any reliable evidence (from studies etc.) of which standard
should be used?

Cheers
Mike