Conditional Formatting: Custom Colors
Custom colors are now available in conditional formatting. In addition to the predefined color options, you can now select "Custom" which opens a full color picker. There, you can define colors using RGB, Hex, or HSL values, or simply choose your desired shade using the integrated color picker.
This allows you, for example, to apply precise brand-compliant colors (CI colors) — for maximum flexibility in visually designing your project and task lists.

Help article: Conditional Formats