Shalom u’vracha,
Strictly speaking, a woman may be betrothed with any ring, whether silver or gold, whether white, yellow, or red gold.
However, the Ben Ish Chai wrote that, according to sod, there is significance in performing kiddushin specifically with a silver ring, because silver corresponds to chesed, and the ring symbolizes the encompassing light that the woman receives from her husband through the kiddushin.
In practice, some have the custom to perform kiddushin with a silver ring. However, most people customarily perform kiddushin with a white-gold ring. Each person may follow his preference and custom, as there is no halachic requirement in this matter.
One important point, however, is that the woman should know what material the ring is made of, so that she does not think it is white gold when it is actually silver.
Most importantly, may it take place at an auspicious and successful time.