Well Martz, Hostas leaves turn white not only because of the excessive or dim sunlight but also there are certain varieties of this plant available following a certain trend like in some cases the whole leaves become albescent or just the centre or the margin. I think you should check for what plant type have you got.
Juliaa is correct. In addition, too much or too little water, infection, and tiny munching bugs can also cause chlorophyll production to cease. Take a sample to a garden shop for a diagnosis.