I have two yo yo loaches in my tank, each of them are about 2 inches long. One of them is very distinct and distinct in its coloration between the black and gold markings. The other one however seems to have a "faded" dull look to it. Both are still very active, even in the daytime, and eat well and have not changed their demeanor at all. I can not find any other signs of distress of unhealthiness. Is this coloration a disease or some sort or something I'm doing wrong? Please help I love these guys and would hate to see them upset or worse dead. Thanks