Based on the pictures, they have similar markings to what I have experience with brown blood disease.
I have fixed a wide variety of problems by adding salt...Epsom salt from the old people section at local pharmacy to water and increasing aeriation. I am not saying that's what your problem is, but I have seen it work wonders on mine.
Based on pictures look at your water.....something is wrong with your water. Once you determine what the specific problem is, look to cause.
I can guarantee you though it's your water. Have you tested it? What is your dissolved oxygen reading?
When stressed, fish stop eating and change color. Do you have labored gill movement and/or gulping action at surface?