I bought discus from JMS a few months back and after 24 hours i noticed that they had gill flukes and what turned out to be discus plague. They told me at the time that the fish were fine and them being dark was normal and as they settle into their new tank they will get colour. This was incorrect and caused my whole tank to be infected and caused them all to die =(. I have now found another aquarium that know what they are talking about when it comes to discus.