If the band is brand new and the stains or discoloration were present when you received it, I would not try using any cleaners or other methods to remove them.
If you purchased the band directly from Apple, Apple generally provides a 14-calendar-day return period from the date you received it. I would recommend returning or exchanging the band through Apple rather than attempting to correct the problem yourself. If you purchased it from another retailer, you would need to check that retailer's return or exchange policy.
You can also take the band, along with your proof of purchase, to an Apple Store and have them examine it.