My snail's shell doesn't look right, it's lost its color. Does anyone know why that would be? Is it a sign of illness?

It sounds to me like a sign of ill health. I don't know about aquatic snails but I know with land snails they might have discoloration due to mites...that's obviously not an issue with aquatic snails but it could be another type of parasites (worms)? Or from malnutrition? Or yes, an illness of some kind.

Are there any other signs? Is he eating? Lethargic?