Decide on a convention for discussing and representing colours in gitlab, Figma and developer implementation

On desktop, we have new colours coming from Mozilla. See #43688 (closed).

We have a few issues, which we can try and solve.

1. New colours are defined in the Oklab/Oklch colour space

The new colours are defined in terms of the CSS function oklch. This probably has improved results, but does make it harder to express them in terms of the usual RGB. Which may make it harder to communicate between applications and UX team.

To try and address this, we could try and communicate primarily in terms colour names, so "blue 40", "purple 20", etc.

The other thing we could do is produce a HTML reference page which maps the colour names to the corresponding RGB colour values. See https://people.torproject.org/~henry/colors.html.

Another note is that Gitlab won't produce a little colour preview for us, like it does with #fba6c5, but I think this only a minor loss.

2. No reference HTML page from mozilla

The new colours are in mozilla-central, but not yet in Mozilla protocol or the Acorn colour list.

Can we find out when they are planning on doing this?

Otherwise, we can just have our own reference as mentioned above, and have more control over this.

3. Figma colours

Should Figma be using the oklch values as well?

4. Android is using old colours

As far as I can tell, these changes in colour are on desktop only, so Android is still using the old colours.

We should try and find out what Mozilla plans to do on android. If android has a different colour palette, then do we want a separate colour palette on Figma for desktop and android?

Otherwise, if we want android to use the same colours as desktop, we would need to convert them to RGB anyway for android developers because as far as I know we cannot use the oklch colour space on native android.

/cc @donuts @felicia @nicob @boklm @brizental @clairehurst @dan @jwilde @ma1 @morgan @pierov