discoloration

US /dɪˌskʌl.əˈreɪ.ʃən/
UK /dɪˌskʌl.əˈreɪ.ʃən/
1.

verkleuring

a change to the original color of something that makes it look unpleasant or damaged:

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Too much fluoride can cause a harmless discoloration of the teeth.