Yellow tooth

Can someone please offer advice?

LO is 13months and has 8 teeth. One tooth has a yellowish tinge, not very yellow but noticeable. We brush her teeth 3 times a day and her other teeth are all sparkling white. I don’t get it. Could it be something serious rather than plaque build up? Worth going to the dentist for? (I would like to avoid unnecessary trips to a dentist in these times)