There is another forum thread with good info, you might look at that. Mold comes in lots of different colors, depending on what's in your region so the orange color is probably not the issue. If it is on lumber planed at 15%, then at some point that board was above 15% after planning (for example condensation within a package) or perhaps the board was adjacent to a wet board in the unit and the surface was wet enough for mold to grow.