What do black speckles in baby poop mean? Is it normal?

My baby is 6mo she has acid reflux so she's on baby Zantac (1 wk ago). Two wkd ago I gave her colic calm ( usually makes her poop dark). So yesterday and today 3diapers total.. She had dark almost black speckles in her poop?? I called the dr the nurse told me sometimes baby have weird poop, If beh is normal then not to worry but of it's concistent then I would have to take her in.. Well of course I'm worried has this happened to your babies before?