Mould growth can be recognized by appearance and texture (a magnifying glass can help). Generally, mould growth could appear as fluffy, velvety or hairy spots or patches of various colours.
Mould growth may not be visible at the early stages of growth or if it is of the same colour as the surface on which it is growing. If a material susceptible to mould growth has been damp for a few days, chances are that there is some mould growing on it even if it is not visible.
If not sure whether what you are looking at is mould or not or you want to know what species (type) of mould is growing in a building, you can send samples to a lab for testing. Click Mould Testing Lab for details.
If interested on how you can recognize mould in a buildings or how you can interpret laboratory results, click Mold Training for details.