Re: Use of colour

Hi Brian

Just to clarify, I'm looking at the contrast between the black text and the white text to ensure that the difference in hue is sufficient to act as a change in lightness for the use of colour sc.

Please can you advise on how to calculate the difference in contrast between the white text and black text taking the background colour into account. I don't think there's guidance re calculating lightness directly?

Thanks

Sarah

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________________________________
From: bryan rasmussen <rasmussen.bryan@gmail.com>
Sent: Thursday, July 13, 2023 12:40:50 PM
To: Ms J <ms.jflz.woop@gmail.com>
Cc: w3c-wai-ig@w3.org <w3c-wai-ig@w3.org>
Subject: Re: Use of colour

Yes, the background is important as to whether or not the color has enough contrast, contrast is related to both the color and background it is on.

On Thu, Jul 13, 2023 at 1:29 PM Ms J <ms.jflz.woop@gmail.com<mailto:ms.jflz.woop@gmail.com>> wrote:
Hello

Please can someone advise on use of colour.

I understand a change in hue of at least 3:1 contrast should indicate a sufficient change in lightness.

However, is this dependent on the background colour staying constant? For example, if a focus indicator is a change in text colour from black to white, does that pass use of colour? The example in the screenshot I have attached says it does not pass (from the non-text contrast guideline). The change in text colour if you measure directly, white to black, does exceed 3:1. I would have thought this passed?

Does it matter that the buttons background colour also changes? Does this break the ability to compare the lightness by just comparing the colour contrast ratio and checking it exceeds 3:1?

Thanks

Sarah

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