Hi
Apple's recommended steps for cleaning the Sport Band are to:
- Remove the band from your watch;
- Wipe down the band with a nonabrasive, lint-free cloth;
- If required, the cloth can be lightly dampened with fresh water;
- Dry the band thoroughly with another nonabrasive and lint-free cloth.
To avoid stains or damage, it is important to always keep Apple Watch and the band clean and dry in accordance with the cleaning and care instructions (including cleaning them after workouts or heavy sweating). Apple also advises that band colours may vary or fade over time.
If you are concerned about a potential manufacturing defect, contact Apple Support (mail-in service may be available) or make a Genius Bar reservation with a view to having the band checked under warranty:
https://www.apple.com/support/watch/contact/
Note that trying to clean the band using abrasives or cleaning products is outside Apple's published guidelines, so may render the band ineligible for warranty service.
More information:
Change your Apple Watch band - Apple Support
Cleaning and wearing Apple Watch - Apple Support
https://help.apple.com/watch/#/apd707b42a5e