Improve the "Add title..." and "Write" placeholders color contrast ratio

[afercia]

The new "Write placeholders" have an insufficient color contrast ratio. To be compliant with the WCAG at level AA, text should have a contrast ratio of at least 4.5:1 with its background.

If I'm not wrong, the current color is #ccd0d4 and gives a result of:
Luminosity Contrast Ratio: 1.55:1
https://jdlsn.com/color/?type=hex&color=ccd0d4&color2=ffffff

The only exception is when the text is bigger than approximately 24px or bigger than approximately 18.5px and bold: in this case, the required contrast ratio threshold lowers to 3:1.

The "Add title..." placeholder has a (computed) font-size of 32px but the color contrast ratio is just 2.93:1 and should be at least 3:1.

Note on colors:
I guess colors should be picked up from the new ones designed by @hugobaeta, https://codepen.io/hugobaeta/pen/grJjVp not sure #ccd0d4 is there. I see the implementation sometimes uses a CSS generated content and sometimes a placeholder attribute, that's perfectly fine but worth nothing the current styling for the placeholder attribute is overriding the rules provided by core:

they were introduced in https://core.trac.wordpress.org/changeset/36619 for good reasons. Maybe worth considering updating the core rules with a new (and accessible) shade of gray.

[jasmussen]

Nice. Looking at https://github.com/WordPress/gutenberg/blob/master/editor/assets/stylesheets/_variables.scss, what would be the lightest Hugo gray that would pass the test?

[afercia]

Against a white background, I think it's #6c7781 which gives a 4.57:1 contrast ratio:
https://jdlsn.com/color/?type=hex&color=6c7781&color2=ffffff

[jasmussen]

I could accept that, but wouldn't #7e8993 work also? https://www.joedolson.com/tools/color-contrast.php?type=hex&color=%237e8993&color2=%23ffffff&alpha=1 — that gives a > 3:1 contrast ratio, which you suggest should be the least.

I suggest this lighter color not for the visuals, but rather, I'd like for it to truly look like placeholder text, and not be confused with actual text, and the lighter we can make it, the better for that. If #7e8993 passes, even if not with flying colors (pardon the pun), I'd vote for that.

[afercia]

A 3:1 contrast ratio conforms to the WCAG level AA only for text bigger than 24px or 18.5px bold. So, #7e8993 is OK for the big "Add title..." but not sufficient for the smaller "Write your story/Write".

[jasmussen]

Ah understood.