My Orchids Look Yellow
It is hard to say exactly what is wrong.
It could be over watering:- are your orchid pots wet? dig your fingers into your potting mix. Are your orchids rotting, leaves pulling out or canes going mushy. If so have a look at the "Watering" section for more information
It could be that your orchids need repotting:- Good potting mix may last up to 4 years, although a lot of mixes used for "Gift Lines" will need repotting after flowering. They are normally potted in a very cheap potting mix/sphag/rockwall/foam.