Colour contrast algorithm when black is used

There recently was a Twitter discussion about colour contrast combinations.

https://twitter.com/davidmacd/status/899215930445754368

There seems to be consensus from stakeholders that when black #000000 is
contrasted against some colours, the 4.5 threshold is met even when it's
hard to see. I've noticed this for years, and it seems others have too, but
the Twitter discussion got me thinking about it again.

Black against #777777 passes, and black against dark orange passes, but to
the eye, white #FFFFFF which fails, seems much more readable against this
grey  or against this orange.

There is something about black #000000 which needs a little tweak in the
algorithm.

Perhaps when black is against colour spectrum X, it requires a higher
contrast minimum?

I'm thinking about an amendment to 1.4.3 in 2.1. It would not be a new SC
so we wouldn't have to get it in before the 22nd.

The discussion is active and I hope to come back with a concrete simple
amendment soon.

Cheers,
David MacDonald



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