Jason gave the answer. A great answer. Yes, a colleague is someone in your professional field, but not necessarily someone you work with in the same company. A co-worker is always someone you work with and normally involves non-professional work. As a lawyer, I can say my opponent on a case is my „colleague“ (even though my client would call him the „enemy“), just because we‘re in the same profession. We couldn’t even legally be opponents on a case if we worked for the same law firm. But, if I worked in a supermarket stocking shelves and some other guy was there doing the same thing along side me, working for the same market, he‘d be my co-worker.

They mean generally the same thing, but a co-worker is always in the same company as you are. Colleague is a broader term; everyone in your field is technically a colleague but it is most often used to describe professional or academic fields. Someone in a low-wage job would not refer to their co-worker as a colleague unless they were making a joke.

Essentially there is no difference both words mean the same thing. However, some people might find it more pleasant to be addressed with the term "colleague" as opposed to "coworker" because there is a little bit more intimacy in the word. Although colleague means "someone for who you work with," most English speakers will take the use of the word a different way. They will acknowledge the term colleague as a substitute for the phrase "friend for whom I work with." Essentially both words mean the same thing.

I agree with both 니코 <3 and Jason.