Support monotone brand colors on the SDK

Is your feature request related to a problem? Please describe.
If I want to use a monotono color scheme. i.e Brand Color is Black/White based on the theme. The SDK doesn't work well when th brand and text-primary are set to the same color. In the buttons we have the text, which is text primary, and then the background color of the button is based off the brand color. This works fine if brand and text-primary color are different, but if they are the same color it doesn't.

So I expect the foreground color on buttons (black on white) to be different than foreground on background (white on black)

Describe the solution you'd like
Support this type of color system, so shifting text color in a way that guarantees better contrast.

Describe alternatives you've considered
None since the foregrounds (checkbox's check mark and the button's text color) are hard-coded, and are different than the text-primary color (which I set to white because my app is dark mode)

Additional context

There is more context here https://metaboat.slack.com/archives/C06FCQT0KMZ/p1763384940043469?thread_ts=1763379377.871829&cid=C06FCQT0KMZ

No files or tests are named. Start by locating the SDK button and checkbox foreground-color handling described in the issue, then trace how brand and text-primary theme values reach those controls. Done means monotone brand themes produce distinct, readable foreground colors for buttons and checkbox marks, with coverage for both light and dark cases.