Is it flat and skin like? Is it shiny under a light?
If it sounds like this, and isn't raised or cotton-like, it may be an iridophore. These are harmless spots of shiny skin that are very common in all colours of axolotl - my Wildtype has them all over her back and tail, my Golden Albino has them particularly on his tail. If this is what it is, then there's no need to worry. Iridophores are completely normal. But do keep an eye on it in case it turns out to be ick (white spot) but I'm sure you'd normally see more than one if this is the case.