Could be either mold or hairs. I have a stain of 'bluberry punch' that has little hairs that are white. To most it looks like mold, but is normal on this plant.

The easiest way to tell is to run your fingers up and down the stem and see if it feels soft or prickly. If it's prickly it's normal. If it's soft and comes off on your finger it's mold. Hope this helps and good luck!

TGT