Draft an implementation of the new palette in GOV.UK Frontend

[Kam-Nijjar]

What

Figure out the most suitable way to make the new palette available for designers to prototype and assess components in the review app, and then turn it on.

Why

Rather than ‘just’ replacing all the colours, we need to think about how this might interact with work to rebuild the govuk-colour map and provide the new palette as part of #6241. See the planning doc on a new palette system (internal).

Is it simpler/better to try to apply the new palette as is now, or build a rough implementation of the planned updates to the colour palette system?

Who needs to work on this

Developer

Who needs to review this

Designers

Done when

• We have decided the best approach for applying the new palette for prototyping
• We have created a branch with the new palette, including instructions on how to use it

[owenatgov]

We now have a PR to work off for this in #6266 so this is done!