Buffalobo, my suggestion is to start with a good field guide. The only one I recommend for a primary guide is the Sibley Guide to Birds, 2nd edition. Other guides can be useful for further study but this is the best.
https://www.amazon.com/Sibley-Guide-Birds-2nd/dp/030795790X
If you want more detail about hummingbirds I recommend A Field Guide to Hummingbirds of North America:
https://www.amazon.com/Field-Hummingbirds-America-Peterson-Guides/dp/0618024964
Sibley will give you enough to ID most birds. I don't use any particular ID websites but there are countless ones out there. A good friend has
http://www.hummingbirds.net, and it's pretty good.
In Colorado, hummer ID is pretty simple as there are only two breeding species normally found in the state, the Broad-tailed Hummingbird of the mountains, and the Black-chinned Hummingbird of the plains, suburbs and dry mesas. Broad-tailed can be seen anywhere in migration. A very small breeding population of Ruby-throated Hummingbirds is likely present around Lamar.
The only other
regular hummingbird species are the migrant Rufous Hummingbird and the Calliope Hummingbird. With rare exception both are seen only in the fall or southbound migration beginning around July 4 through mid September.
So, search on the four regular species and you will have ~99.9% of the hummers in CO. As you delve into the ID you'll find that each species, sex and age have different characteristics of plumage, flight pattern, wing sounds and vocalizations. That's where the fun and challenge is. I usually can ID CO hummers to species and sex and sometimes age with my eyes closed as they fly by from their wing sounds and vocalizations alone.
Oh, if you know of any other species in CO, I want to know about it. Part of my work is documenting rare, out of range and out of season species.
Good luck!