This is a moisture mold due to lack of UV light (from lack of Sun), and it is usually harmless to the seedling. This may occur if the globes are placed near the window and get very hot, during the germination period, before the seedling has sprouted. Moisture mould can be eliminated by spraying a little hydrogen peroxide or the suns UV rays will kill of the moisture mould as well.
Once the seeds start to germinate you should remove the top half of the globe used to cover the growing pot and place the seedling in a well lit area so that it receives lots of sun light. The edges will dry out and any mold will disappear.
If you have lots of mold you can:
Use a mixture Hydrogen Peroxide dilted with water (only 3% Hydrogen Peroxide). Hydrogen Peroxide stimulates oxygenation in the
soil and also encourages increased root growth. This is the best method.
Or use vinegar diluted with water in a spray bottle (10:1 ratio of
Water:Vinegar). You don't need to use much.
Another option is to use ultraviolet lights to dry out the pot and give it a heavy dose of UV light.
If you are really worried about your seedling then please send us an email with a photo so we can assess it for you. email@example.com