The contrast warning recommends a colour that passes

When a colour you pick is too faint for the surface it sits on, the warning under the colour field now ends with a recommended colour, such as "Recommended colour: #767676."

• Text (action text, visitor text, links and the like) is checked against 4.5:1.
• Icons and borders (action buttons, suggestions) are checked against 3:1.

The recommendation is the smallest change that passes: the first step toward black (or white on a dark backdrop) that reaches the threshold.

The field never blocks saving, and the colour is applied as you set it.