Additional features, settings, or issues not covered by specific Microsoft Teams categories
Unfortunately, AFAIK, you cannot change the specific colors for progress statuses in Microsoft Planner. The colors for "Not Started," "In Progress," and "Completed" are locked into the system.
You can, however, customize your board by using color labels instead. To use labels, click on any task to open its details. Look for the label section on the right side. Select a color block and click the pencil icon to give it a custom name. You can use these names to show different types of work.
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hth
Marcin