USWDS Color: Add luminance checking into testing and CI. #3400
Description
Description
As a USWDS contributor I want to check that the color passes accessibility. Add color test in npm test and into CI.
We want to be sure a color family passes:
| Color Difference | a11y Baseline |
|---|---|
| 40 | ✅ AA Large |
| 50 | ✅ AA |
| 70 | ✅ AAA |
The strictest check is AAA, if a color passes with a difference of 70 (AAA) then we don't need to check AA & AA Large.