Reason for one tooth to be slightly more yellow than others? (Photo)

My right lateral incisor is a bit more yellow than my other teeth. Had braces as a teen but no trauma. (I'm 50 years old). Has been this color for years. No pain on biting or percussion. Responds to cold but takes longer to respond than my other teeth. Just had my regular check up and asked my dentist about it (same dentist for 20 yrs). She said it's likely extra dentin deposit. I also just had x rays taken for ortho treatment due to relapse but ortho didn't say anything. What might cause this?