Full sun will cause leaves to lighten up in color as opposed to a dark green color if grown indoors.

Also, watering issues can cause yellowing of leaves, usually too much water.

Nutrient issues can also be the cause. I had a Sabal uresana with the above condition that was nearly white and declining. I repotted it in a more palm friendly mix and added epsom salts and iron chelate. It greened up within 2 weeks.

Hey if you don't know which one worked but what you did worked,do it all again,or you could try chelated iron,ferti-lome makes some with iron,manganese,copper and zinc