Ensure editor color palette provides accessible contrast

[Ovgodd]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.

The color palette offered by the editor contains colors whose contrast ratios do not meet the required accessibility thresholds.

Some colors can produce insufficient contrast when applied to text, especially against light or dark backgrounds.

No indication is currently provided to the user about whether the selected color is accessible or not.

This can mislead authors into creating inaccessible documents even when they only use the default editor palette.

Describe the solution you'd like

The default color palette should only contain colors that meet contrast requirements.

Expected contrast thresholds:

4.5:1 for normal text
3:1 for large text and UI components

If users can enter a custom color outside the default palette, a warning should inform them when the selected color does not meet the required contrast ratio.

Example warning:

<div role="alert" aria-live="assertive">
  Warning: this color has insufficient contrast (ratio: X:1).
  A minimum ratio of 4.5:1 is required to ensure accessibility.
</div>

The goal is to help users create accessible documents by default.

Describe alternatives you've considered

Another option would be to keep the current palette and only provide documentation about contrast rules.

However, this would put too much responsibility on authors and would still allow non-compliant colors to be offered by default.

A better approach is to provide compliant colors by default, and warn users only when they choose a custom value that may not be accessible.

Discovery, Documentation, Adoption, Migration Strategy

Steps to reproduce:

1. Select text in a Docs document.
2. Open the formatting menu.
3. Open the color palette.
4. Choose a color from the proposed palette.
5. Check the contrast ratio with a tool such as Colour Contrast Analyser.
6. Notice that some palette colors produce ratios below the required thresholds.

Expected behavior:

• default palette colors meet contrast requirements;
• custom colors are checked when possible;
• users are warned when a selected color has insufficient contrast;
• the warning is announced to assistive technologies.

Additional context:

Authors are responsible for their editorial choices, but the editor should not provide non-compliant choices by default without any warning.