If you're not seeing bugs (and the damage is really too large to be bugs), then I think what you have there is just a genetic anamoly, meaning it's an issue that comes from the plants genes in parts of the plant that are affected. This is unusual and I've never seen it before, but because you have a light green color, I'm guessing that some of the tissue is present but not all of it. This is kind of like when I person is born with or develops a discoloration of their skin in certain areas. The tissue is different such that it shows a different color. If you're not seeing bugs and can't determine how the leaves got damaged, it's probably a result of a genetic malfunction. You'll know for sure if the problem doesn't spread or get worse. Frankly, I don't think it will be anything to worry about.