Hi , I looked at mine , the lower leaves on it are a lighter color . Mine might be a smaller plant it is the bottom 2 on it . I think they are just getting tired , they seem to go south at a slower rate than the Hybrid leaves .
How many leaves total are there on your plant ? if there are not a lot more than 4 then it might be to much light . Mine is under artificial light and is back from an east window , but is not as close to the fixture . Hope this helps a little . Gin