Downarrow above player's heads

When playing the match, sometimes when I'm running from spawn to the fight I can't see my teammates' names, but I can see a little downwarrow that hovers over their names. Sometimes it is blue, but sometimes it flashes orange, then they die, or it just returns to being blue, and sometimes it switches so quickly I'm not sure what it means.

What does it mean for the down arrow above player's heads when it turns orange or blue? Is it an indicator for their health bar or something else?

A blue chevron indicates a teammate that is not currently "in combat".

A hero becomes "in combat" when they damage the enemy or are damaged by them. In this case the chevron turns orange. I have witnessed orange chevrons over green-outline teammates multiple times when playing halers, so it is not tied to health.

Lastly, a green chevron indicates someone in your party.

Yes.

Blue arrows indicate a full-health teammate, yellow indicates someone who has taken damage, and orange indicates someone at 50% HP or less.