Why are my Phrag Hanne Popow leaves so yellow?

[Joella]

Hi everyone, I am new to the Orchid Board and I have a question for s/h orchid growers out there. I have a seedling Phrag Hanne Popow that has been in s/h for about 2 months. It's large enough that's it's bloomed already, but still pretty small. Anyway, lately the plant has been looking fairly yellow. The roots are all healthy looking and it is starting a new root and a new small new growth. One lower leaf is fairly yellow but does not appear ready to fall off, the rest of the plant also has a yellow tinge. Does not appear to have crown rot. Does anyone know what would cause this? I was thinking water quality and have been using distilled water lately but I can't tell if it's helping since the plant is still yellowish. I used neem oil on the plant when I first got it, as I do with all new additions, and have never had problems before. It sits next to phalaenopsis and paphiopedilum which do not have yellow leaves, so I'm thinking it couldn't be getting too much sunlight. Any ideas or suggestions? Thanks!