What kind of features does the knife have to posses to be considered a Switchblade?

I guess what I'm trying to get at is that, I was charged for possesion of an illegal weapon for a knife I have owned for about 3 years. I have been searched by police in the past and have been given the knife back without any incedent, but I guess it depends on the cop you run into. The knife I owned I guess I never considered a switchblade, I mean I does have a on on the side of it to make it pop up, but is no longer than 3 inches. I considered it myself a pocket knife. It would be helpful to hear from anyone who has experinced the same thing. By the way, I live in Colorado and I know the laws are different from state to state.