Customizable background colors when using the color theme

[jattasNI]

Brandon's vision for the color theme has been monochromatic (white) components on top of any dark background color. Our current implementation hardcodes a specific color in each of the background color tokens. We should design an API to support client applications changing the color theme background color.

Open questions:

1. would it be the same accent color for all the background tokens?
   • application
   • header
   • section
   • divider
   • tooltip
   • various calendar events
2. what would the API be? Would the accent color could be set on the theme provider or would it require a more complex set of token values? (informed by the answer to 1)
3. do we want a new "light color" theme that supports arbitrary light background colors? This would require updating tokens for most component foreground colors vs their current values in the existing color theme.
4. As a stopgap, can we just change the default green background color to match the one that this client needs? Would doing that cause acceptable impacts on existing users of the color theme?

This came up in the context of the chat components wanting a different green background color (Digital Green Dark) on the input toolbar for better contrast.

[jattasNI]

A possible stopgap is to change the default green background color to match the one that this client needs.

Open questions before doing this:

1. Would doing that cause acceptable impacts on existing users of the color theme? (SLE landing page plus any others we find)
2. Is this client going to switch to use a light theme toolbar instead, making this work moot?
3. will this client end up building a custom toolbar with a hardcoded non-theme-aware color anyway, making any of our changes unneeded? This might be the case if their use case doesn't call for a toolbar or if they can't get nested theme providers working.

We'll wait for confirmation from Brandon / Jose before working on the stopgap and answering these questions.