CO is what is a "1-party consent" state. What this means that as long as the person recording a conversation is a party to it, then the recording is legal. Conversely, if the person is not a party to the conversation, then recording it is illegal. Additionally, in virtually all states, the law makes an exception for in-person communications when the parties do not have a "reasonable expectation of privacy". So for example, it would be legal to record a conversation in a public place where it might reasonably be overheard, even if you were not a party to that conversation.So depending on where you record matters. If it is within your co-worker's office you should be a party to the conversation. If it is in the lunchroom, hallway or other public area, then they have no expectation of privacy so you need not be a party to the conversation to record it. That having been said, your employer may take a dim view of your making recordings in the workplace. So make sure that you can live with the consequences of your actions. Whether or not the recordings are legal, you might be terminated for making them depending on the circumstances. At this point, you may want to consult directly with an employment law attorney in your area and go over the details of your case. They can then best advise as to your rights/remedies.