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?