@beenthere
It has been estimated that about 300 different genes (in a typical plant) can cause chlorophyll deficiency - meaning that the normal green colour of the plant will be affected if the gene is abnormal. Only some of them will produce albino seedlings. Others may change the leaf colour from normal green to pale green or greenish-yellow, for example. Yet others may allow the plant to have a normal green colour in some circumstances but not in others. Some may cause the leaves to become yellow at low temperatures, others at high temperatures, or may allow the plant to develop more normal green colour at low temperatures or in shade, etc.
It
may be possible that your seedlings might have become a more normal green colour if the temperature at which they were growing was lower (or higher) or if the light was more intense, etc.
