Color palette in Table Cell Properties (Advanced → Cell Properties) cannot be customized or overridden in TinyMCE

📝 Provide a description of the new feature or improvement

TinyMCE currently provides a fixed, built-in color palette inside the Table → Cell Properties → Advanced dialog.
There is no supported way to customize or override this palette through configuration, plugin options, or an external palette definition.

This feature request is for TinyMCE to support a customizable color palette for table/cell color pickers, ideally via a configuration parameter, plugin hook, or JSON palette file, so that integrators can define a unified color scheme.

🫶 What is the motivation?

Large platforms (such as Moodle LMS) embed TinyMCE and often require consistent branding and accessibility-compliant color schemes across the entire system.
Without the ability to specify a controlled palette, users encounter inconsistent styling, and administrators cannot enforce design standards or organizational branding.

Allowing customization would enable implementers to align the editor with corporate design guidelines and improve usability for end users who rely on a predefined set of approved colors.

🔗 What is the consequence of not having this feature?

Inability to enforce a unified color palette across the platform
Users apply incorrect or non-standard colors
Accessibility and design inconsistencies accumulate over time
Integrators have no supported method to intercept or override the built-in palette
Platforms relying on TinyMCE cannot meet branding or WCAG color compliance needs through the editor UI

🚦 How important would you rate the requested feature or improvement?

Important

This does not block editor functionality, but it significantly impacts design consistency, accessibility standards, and branding requirements across large deployments.

Start by locating the Table → Cell Properties → Advanced dialog and tracing how its built-in color palette is defined. Determine the supported customization approach and add coverage showing that an integrator-provided palette is used, with the issue's branding and accessibility requirements reflected in the completion criteria.