No one's answered you and there are several things I can pass along since I'm a "master gardener" - though that doesn't apply as much here as my experience. I have grown avocado trees from pits successfully numerous times. What you're seeing here, in my opinion, is mold. I suspect you're exposing the pit to too much water.
After removing all the flesh from the pit, preferably using your hands and then a cloth to avoid damaging the pit, rinse it thoroughly under warm water and wrap it in a damp paper towel and stick it in an open ziplock bag in a dark place. I don't recommend the toothpick method.
After 4 to 6 weeks, occasionally re-dampening the towel, you can bury the pit in a small pot. It may take a little longer than 6 weeks for the germinating pit, or seed, to be ready. You'll know it's ready when the root coming out of the pit is nice and strong and ready to hold the plant, growing at least an inch outside the pit.
Bury the side down that's where the roots come out. Leave about a third of the other side of the pit above the soil. Well drained soil, typically called "cactus blend" or "cactus soil," is great, although everyday "potting soil" will work alright. I don't recommend using fertiliser at all in the first year. The seedling digests the pit as it grows.
In the first year, I recommend using a pot just a little larger than is needed to hold the plant and its roots, possibly no more than 10 in tall x 5 in diam at the mouth if using a custom-made one or slightly smaller if using a standard-sized pot. This is necessary so that water will focus over the little avocado tree's roots well before draining well when you water it. Transplant it into larger and larger pots as it increases in size.
Anyway, there is sometimes soil between the pit and the little plant when you first plant it. You'll see what I mean. I don't have any growing right now to take a picture of.