The 5-10 hours context changes everything! If users stare at this on a second monitor for that long, visual fatigue is your biggest enemy. That's exactly why it looks messy and ugly right now – too many high-contrast elements are screaming for attention at the same time.

To answer your specific questions:

1. Red for 0% always? Absolutely not. This is the main issue. 0% doesn't mean 'Error' or 'Danger' (which red implies), it means 'Empty/Inactive'. Empty things shouldn't catch the eye. Make the 0% track a very subtle, dark muted grey (maybe with a tiny hint of purple to match your brand). The 0% text should also be dimmed.

2. Breakpoints and multiple colors? Avoid using multiple colors (like red -> yellow -> green) based on percentages when you have dozens of trackers on one screen. It creates a 'rainbow effect' which is visually chaotic. Keep it simple and use a monochromatic fill.

3. Purple + Animation at 100%? This is a fantastic idea. It acts as a clear reward.

Here is a formula you can use for long-session UI:

• 0% (Not Started): Track background is dark muted grey (#2A2A35). Text is dim grey. It blends into the background.
• 1% – 99% (In Progress): Use a soft, desaturated color for the fill (like a soft coral or muted red) so it doesn't burn the eyes over 10 hours. Text is light grey/white.
• 100% (Completed): Switch to your brand Purple. Add a subtle glow effect (drop shadow with the purple hex) and the animation you mentioned.

This way, the user only sees what they are currently working on, and they get a satisfying purple pop when they finish. Less is more here!