[css-color] Privacy considerations should describe how system colors are chosen in practice

[jyasskin]

https://drafts.csswg.org/css-color-4/#privacy currently consists entirely of

This specification defines "system" colors, which theoretically can expose details of the user’s OS settings, which is a fingerprinting risk.

The likely amount of fingerprinting depends on the distribution of users' choices of system colors. If operating systems encourage users to pick from one of 8 palettes, there's much less risk than if the operating system infers an accent color from the user's personal background image.

There's debate about whether even 3 bits is too many, or whether fingerprinting is a lost cause, and so we should be willing to expose a color that's unique to a single user. To help the various positions in that debate decide what to ship and under what restrictions (e.g. only installed apps?), it would be good for the spec to describe what we know about the actual distribution of system colors.