Any one or several factors would cause leaves to discolor, including bugs, pathogens, lack of nutrients, moisture and overheating.

Pictures would help, as would some indication of how much sun, water,and nutrients they are getting. Are they being propagated in a greenhouse or conservatory, or newly purchased and not yet planted? What kind of laurel are they?

Are the polypockets big enough for the laurel plants? They are usually small and laurels grow very big.

Lack of sufficient nutrients and water. I've no idea what you mean by 'polypockets' in a gardening sense (to me, they're clear document holders for ring-binder files) but whatever they are, they sound far too small to contain Laurel plants. Laurels need to go in the ground, or in a large pot or other container.