Goldfish loosing color

Hi everyone, Hope you all are well. It’s been a few weeks since I dropped in. One of my bug eyed goldfish was pure black. Over the past few months it’s loosing color and turning golden color. Is this normal? I think the name of the breed is fantail. The other one just like it doesn’t seem to be changing. Do you think one could be a female and one a male? I hope so. Maybe I’ll get lucky