[Bug] Trademark Policy uses term "contrast ratio" without defining it

[SamB]

Description

The Trademark Policy says:

You are not authorized to use any modified versions of our trademarks, except that you may use a different color for the CC logo and its background so long as the two colors chosen have a contrast ratio of at least 3:1.

But what ratio do you mean? For web use, do we …

1. … just add up the 8-bit RGB components of each color and then divide?
2. … realize that the amount of illumination corresponding to those RGB components isn't actually linear, but something much closer to sRGB, so convert to CIEXYZ color space?
3. … remember that human perception isn't linear, so convert to e.g. CIELAB color space instead?

… and what about viewing conditions?

I suppose we could try to use the definition at https://www.w3.org/TR/WCAG21/#dfn-contrast-ratio, but see w3c/wcag#695 for why that might not be the best plan.

And what about usage in print?

In conclusion: (╯°□°）╯︵ ┻━┻. It might be better to forget about defining things for now, and just say something like "but please choose colors with plenty of contrast".

Resolution

• I would be interested in resolving this bug.