Is it bad if a goldfish has one white eye and the other black?

No, it is not bad if a goldfish has one white eye and the other black. This is a common condition called heterochromia iridum, which is caused by a difference in the amount of melanin (the pigment that gives color to our eyes, skin, and hair) in the two eyes. Heterochromia can be caused by genetics, injury, or disease, but it is usually not a serious health problem.