Many timber products have been pressure treated so they are protected against deterioration by rot or insect attack for many years. Pressure treated timber has been treated with a liquid preservative that has been forced into the wood under pressure. The treatment used is a greeny-blue colour. 

As the timber dries, some of the liquid evaporates and leaves deposits of the treatment salts on the timber surface which manifests itself as green/ blue speckles that can vary in severity. The speckling can be easily mistaken for mould. The pictures below show the difference between mould and pressure treated timber. 

In all cases, the speckled finish of the pressure treatment may be left as over time they will fade. If you would like to speed up the process, you can either pressure wash the timber or lightly sand the affected area. 

Pressure treated timber with some speckling left by the treatment salts	Pressure treated timber exhibiting signs of mould	A light rub down with sandpaper will remove the speckling

If you find that the product is actually mouldy as shown above, this can sometimes happen if products have been stored where air has been unable to circulate which provides ideal conditions for mould growth. Like pressure treatment, mould growth isn't detrimental to the product. The mould will only grow on the surface of the timber as is easily wiped away with a damp cloth, brush or pressure washer. Once the product is assembled and out in the air, the mould will not return.