This is possible with any plywood, especially for plywood panels with higher durability. Durable woods usually contain a higher concentration of tannic acids.
These tannins act as a kind of vaccine against bacteria and fungi that are moisture related. In other words, a positive characteristic! However, they can stain when it rains. Don't worry, this leaching will naturally recede.
Tip 1: Never leave the plywood in the bare sky, in fact, a heavy rain can cause color transfer resulting in a nasty streak.
This streak formation fortunately disappears again by itself. The same phenomenon can be noticed when you place brand new wooden garden furniture on your patio. The first year you will see a brown markings, but after that it will disappear again.
Tip 2: Does the panel remain visible for a piece? Then be sure to apply a lick of paint. This way you avoid moisture from allowing the tannins to leach out.
