Brown goo on Chicken breast?

Last night I bought a package of boneless skinless chicken breasts and one of them had some brownish/greenish goo stuff on it. Usually the goo is just clear. Was there something wrong with it? My boyfriend assured me that it was fine, so I cooked it anyways and so far neither of us have gotten sick or anything.

I am just kind of asking for further reference, also if anyone knew what this stuff was and why it was off colored.

Thanks!