Is the stool test "positive" when there is only a small speck of blue-green color on the test area?

Yes, minimally so: Yes, but may be equivocal. Depends on the circumstance, diet, etc. Worth repeating. If patient is at risk for colon polyps or cancer, by age, family history, or symptoms/physical exam, then the stool test is not the make or break issue in deciding to do further evaluation. If there are other GI symptoms, the decision for evaluation depends on histroy and physical.

Guaiac test +: Guaiac (leuco-dye) testing has been available for >100 years--the colorless dye turns blue or green in presence of adequate amounts of peroxidase-like substances (e.g. Hemoglobin) & hydrogen peroxide. Ingested iron, certain fruits & vegetables, some drugs, toilet bowel sanitizers give false-positive reactions. Method of collection & underlying pathology may account for your + finding--see doctor.