I had a tooth extraction, bone graft surgery 3 days ago. Swelling and pain are horrible, gum is black/grey, dark red lump around it. Is it infected?

Possibly. But without knowing the extent of the surgery or the graft, and without being able to see you, it is impossible to tell. Your best bet is to call the surgeon who performed the procedure and be re-evaluated.
Not via computer. You need to be immediately evaluated by Dentist, Periodontist, or Oral Surgeon that did extraction. You may need additional treatment and/or antibiotics.

Related Questions

Had a tooth extraction and bone graft 3 weeks ago. Yesterday noted swelling and pain. No redness or oozing from site. Possible food irritation?

Possible.. But any swelling or pain should be evaluated by your surgeon. Give them a call for an immediate follow up appointment. Read more...
Possible. Is there any reason why you would not give a simple call to the author of the extraction....he/she would be best to see you as a postop & be able to answer this question quicklly. Read more...
Food trauma. Possibly food trauma. More likely an infection.Have your surgeon evaluate this for medications. Read more...
Definitely, yes. You should avoid popcorn, nuts and seeds and hard food for 6 weeks after your extractions. If concerned see your dentist for evaluation. Read more...