I was told that the kallahs wedding band has to be gold. Is this true?

According to the Torah one can be Mekadesh with Kesef Shtar & Biah [Money, contract & relations]; the Rabbis prohibited Biah because of immorality. The custom is to be Mekadesh with Kiddushin of Kesef, and specifically with a wedding band. The common custom among Ashkenazim is to be Mekadesh with a round gold wedding band. Among the Sephardim the common custom is to be Mekadesh with a round silver wedding band. Some have the custom according to Kabala to be Mekadesh with a silver wedding band that is round on the inside and square on the outside. [שו"ע אהע"ז סימן כו סעיף ד, וסימן כז סעיף א וברמ"א, ובערוה"ש סעיף ב, וע"ע פרטי המנהגים בהרחבה בספר הנשואין כהלכתם ח"א פרק ז, נטעי גבריאל הלכות נישואין ח"א פרק כא].