The width of the progress bar shows what percentage of the actions that should be done today have been done.
The colour indicates whether the higher-priority actions have been done.
- red means there are still actions with a priority for today higher than 100 (i.e. the overdue actions with a priority box in red)
- orange means all the overdue actions are done but none of the actions with a priority for today of 90–100 are done (i.e. the "should do" actions with a priority box in yellow)
- light blue means all the overdue and at least some of the "should do" actions are done
- green means all the overdue and "should do" actions are done (although there still could be some "could do" left, with a priority for today of less than 90 and a priority box in green)
The "could do" actions (those with a priority for today of less than 90) contribute to the percentage but aren't required to hit 100%. It's therefore possible to get over 100% if you've done all the actions you should and have also done one or more coulds.
If you don't have any overdue or should do actions, your progress will always show as 100%.
Hopefully this will give you an extra little incentive to make progress during the day, trying to get the progress to 100% or at least green.