Many variable can dictate what the same hummingbird will look like under different conditions. Body temperature, anxiety level, brightness of the environment and posture can all be factors in how a hummingbird will appear. The different body appearances can also give you a great understanding of the mood or state of mind of that bird. For instance, if a hummingbird has its body feathers ruffled, it's usually in a relaxed state and just regulating its body temperature. If it has it's feathers tight to the body, it's on higher alert. If the tail is splayed apart while body feathers are tight, it's angry and ready for combat.
When trying to identify hummingbirds by appearance, it can be far more difficult, especially if you're trying to find similarities and differences with your regular visitors. Just the turn or tilt of the head can be the difference from a dark throat to a glimpse of red, to a laser beam of red. Birds can be misidentified so easily just by a single factor affecting their appearance.
All 3 of these images are the same Ruby-throat hummingbird. They are all in the same light. It's a sunny day that reflects light off the gorget feathers. The bright light dilutes the color and makes it a bit more rusty/orange. If you had a light cloud cover it would allow natural light to reflect the true color. The following color is from a different time and location, and was also a cloudy day. Those light conditions showed the true and most impressive color. You don't see the bright sun reflecting off the throat, but you do see the the hummingbird in it's most natural appearance. The final 2 pictures are both Ruby-throats, but in different light conditions. Under the same conditions, you'd have to look very carefully to tell them apart, but under these conditions, it's very easy to misidentify at least one of them.