Please don't panic - they're called stress lines, & darken up more often than not when they are stressed or in a different environment. It's totally normal. Don't stop bathing or holding him because of it, that'd be sad
Mirage came out of brumation on April 26. He was doing great. On May 2 he started acting funny. We just redid his tank, and he keeps going into one of his hides. He just lays there. He shows no intrest in food. HELP!