Pride. In one word, it's pride. The Colorado State Flag represents a state that has so much to offer and so many people who love it. If you ever run across someone who says they don't like Colorado, take a picture because you've just found the only one.
So, of course, wearing Colorado flag t-shirt on your chest is a statement. You're saying, "I am Colorado." And you are. I'm sure there is no other state flag represented so proudly by so many.
Note: Not everyone knows what the Coloradi flag looks like, so if you're in the midwest, and you're wearing your Colorado Flag T-shirt, you may be mistaken for a Cubs fan and find yourself explaining your way out of it.