To change the color of a category or project in Amazing Marvin, you first need to open the Master List view. You can do this by pressing "M" on your keyboard, or by clicking on the "Master List" button in the Skinny Sidebar.

Once in the Master List view, follow these steps:

To change the color of a category, click the folder icon. For projects, click the flag icon.

Then pick any color and exit the color picker by clicking outside of it. The color you last picked will be automatically saved. 

You can change the color of a category anytime.

Use your favorite color palette in the settings to get a nice coherent color scheme going.