ive had this happen before. i just got the infection out by sqeezing it. but contacting ur doc is probly the better way to go
sometimes you can get a staph infection when you injure your skin too deep, usually when you cut a hangnail off even its pretty deep it should not turn green, if it does not get better or if it gets obviously worse you need to get some antibiotics, see a doctor, staph can probably spread to rest of body, fever pain chills etc. for the time being keep it clean and covered,
Symptoms=infection.
Consult your physician asap.