Great question! The green stuff you're noticing is algae, and the white is a type of fungus (technically called saprophytic). Although they are totally harmless and unrelated, they do have a similar cause - overly moist conditions. This could be because you live in a humid part of the country, or have your garden located in a humid environment (like the bathroom or very close to your kitchen sink).
Good news is, it's an easy problem to solve!
Just allow your SeedPods to dry out a little more than normal (until they are a light brown color), and the algae and fungus will go away. It's also beneficial to gently remove it with a spoon or similar so that you don't have to wait.
If you're planting your own seeds in the SmallGarden, be sure to place the seeds at the top of the SeedPod so they aren't submerged in water. For all SeedPods (whether our plants or your own), on your first watering start with 500ml, and then once that has been absorbed (and your garden alerts you to add more water), add 1000ml. This combination will help your plants germinate faster and eliminate the potential for mold and/or algae.