‘Silver-tongued’
The term “silver-tongued” is not a reference to color or metal but rather sound. Dating back to at least the late 16th century, the use of the word “silver” here is one that is obscure to us today.
Something is described as silver can mean that it has a melodious sound, such as that of ringing silver. Someone who is silver-tongued, therefore, is well-spoken and persuasive as a result.