Once growth appears, the plate itself becomes a source of evidence. A colony is a clone, so every cell in it descends from one organism, and the visible properties of that clone are stable enough to compare against known patterns. Size, shape, edge, elevation, surface texture, and pigment are recorded systematically, and on blood-containing medium the hemolysis pattern is read as well.
Hemolysis describes what the organism does to red blood cells in the agar. Beta hemolysis is complete lysis, seen as a clear zone around the colony. Alpha hemolysis is partial lysis with green discoloration from hemoglobin breakdown. Gamma hemolysis, sometimes called non-hemolytic, means no visible change. These patterns are properties of the organism, not of the medium, and they narrow the field: a beta-hemolytic Gram-positive coccus in chains from a throat specimen points toward Streptococcus pyogenes, while a gamma-hemolytic one points elsewhere.
Morphology narrows but does not identify. A large, mucoid, lactose-fermenting colony on MacConkey agar is consistent with Klebsiella species, but other organisms can produce a similar appearance, and a small, non-hemolytic colony on blood agar could belong to many species. Colony appearance is a filter that reduces the number of candidates; it is not a species label, and it should never be reported as one.