I had a comment the other day regarding how I tell the difference between the different hummingbirds in the yard. It is somewhat true that they look alike. However, we have been fortunate enough to have a small group of resident Allen's hummingbirds. While some of the marking are slightly different between individuals, especially females, behavior is the main clue to the individual identity of these tiny birds.
The Allen's hummingbirds have divided up the yard into specific territories.
This is "P" (Patio) on her nest. She was a resident for one summer.
Each male has a specific home tree and 3 or 4 specific places that it perches to watch over its territory. Fik was rescued as a fledgling. He knows me and trusts me. I can approach him and get quite close, he in turn will come up to me. He has perched on the same branch, in the same tree, since the first day he learned to fly. Bif perches on the tip of a succulent, he's the only one in the yard that will do that. Canyon is the most timid of the males and rarely comes down in the lower part of the yard.
The females are specifically territorial about nesting sites. These Allen's hummingbird females will nest in the same tree / shrub time and again, especially if they are successful. If it isn't the same tree, it usually is within 10 feet of that tree. One female, DR, (DRiveway) tends to rebuild directly on top of her old nest. She is the only female that has shown this behavior in my yard.
If I saw Fik a block away feeding from some flowers, would I recognize him? Probably not. Coloration can change on birds, from juvenile to mature, from breeding to molting. I have a small group of eight very enigmatic Allen's hummingbirds that live in my yard. They each have their own personalities and behaviors in the yard, that is how I tell them apart.
My friend has 30-50 hummingbirds visiting her feeders during the day. Telling them apart, without bands, would be a completely different matter.