Recall that priority level is a number between 1 and 100 and you can assign it to any subscription in the sytstem in order to group them based on importance rather than type of their published content.
Color coding for priority levels divides this 1-100 interval into 20 equal pieces and each interval is represented by one color in the schema, as shown in the screenshot below. The highest priority level which is the interval between 100 and 96, is represented with the hottest color tone in the scale, that is, color 'red'.
As the priority level decreases, corresponding color tones become closer to the color blue, which represents the least important priority level interval, that is between 5 and 1.
Time-based color coding is heavily used in the ListView of the Subscriptions Panel.