Coloring of activities based on resources

I'm having trouble understanding the behavior of the coloring of activities with respect to resource assignments. Specifically, activities are still showing as orange when I expect them to be green.

Here's my setup to demonstrate the behavior (my real-world case is more complicated with more resources and activities):
- 1 resource, assigned to the project at 100%.
- 2 activities, both set as Duration Driven because they must be completed during a certain timeframe. Duration is 7 days.
- The resource is assigned to both activities at a rate of 20%.

When I set the assigned days to the full duration (7 days) on both assignments, one activity is colored green on the Planning Gantt chart, and the other is colored orange. This does not seem correct, since the resource is only assigned for a total of 40%, less than the 100% allocation to the project.

When I change the assigned days to half the duration (3.5 days) on both assignments, both activities are colored green. This works whether the rate on the activity assignment is set to 50% or 100%.

I'd expect that in both these cases, both activities should be colored green.  Am I misunderstanding something?

 

Yes, I already read that section of the manual before I asked the question. Perhaps I should have stated that.

Why is one task getting colored green and the other orange? From what I can see, they are configured and assigned exactly the same.