Here’s a refined color palette for your calendar application, structured according to your specifications of lightness/value and maintaining the essence of your desired colors. The palette transitions from dark to light to semi-dark, with yellow as the diverging root.

 <Calendar Color Palette> 
1. Midnight Blue - 
          
          #191970
        - A deep, dark blue that evokes a sense of calm and stability for personal calendars.
2. Dark Slate Gray - 
          
          #2F4F4F
        - A strong, muted gray that conveys seriousness for exam dates.
3. Maroon - 
          
          #800000
        - A rich, dark red that represents band events with passion and intensity.
4. Deep Sky Blue - 
          
          #00BFFF
        - A bright, inviting blue that brings energy to time blocks.
5. Slate Gray - 
          
          #708090
        - A balanced gray that serves well for miscellaneous dates.
6. Yellow - 
          
          #FFD700
        - A vibrant yellow that brightens and highlights the academic calendar.
7. Turquoise - 
          
          #40E0D0
        - A fresh, bright shade that symbolizes restful sleep.
8. Light Salmon - 
          
          #FFA07A
        - A soft, warm coral that indicates important events softly.
9. Royal Blue - 
          
          #4169E1
        - A strong, medium blue that signifies tasks with reliability.
10. Deep Pink - 
          
          #FF1493
        - A vibrant pink that stands out for urban policy events.
11. Sea Green - 
          
          #2E8B57
        - A soothing green representing sustainable urban initiatives.
12. Red - 
          
          #FF4500
        - A bold, warm red for band events that demands attention.
13. Purple - 
          
          #800080
        - A classic purple that adds a touch of luxury for recurring events.
14. Silver - 
          
          #C0C0C0
        - A cool, light gray that signifies long-term plans.
15. Fuchsia - 
          
          #FF00FF
        - A bright, bold color for U.S. holidays that pops against other colors.
16. Pink Sand - 
          
          #F4A460
        - A warm, soft hue for course events that feels inviting.
17. Blue - 
          
          #0000FF
        - A classic vibrant blue representing course schedules.
18. Coral - 
          
          #FF7F50
        - A lively coral that adds warmth for important reminders.
19. Cafe - 
          
          #D5C1A1
        - A soft, muted brown that provides a cozy touch for Hokie sports.

This palette maintains the intended dark, light, and medium values, while ensuring a visually appealing transition across the specified categories.

Would you like to adjust any specific colors further, or do you have any additional requirements for your calendar application?