金 and 銀: materials and colors
Distinguish gold and silver as materials from a gold-colored or silver-colored appearance.
Gold as a material
金 is read きん in this guide and means gold. 金でできた指輪 describes a ring made of gold.
金 can also be read かね to mean money. The linked entry here is the material reading きん; use context to choose.
Silver as a material
銀, read ぎん, means silver. 銀の飾りを見ました。 means viewing a silver ornament.
金と銀を比べました。 means comparing gold and silver. It does not specify whether the comparison concerns price, weight, or color.
Composition and appearance
金色の箱 means a gold-colored box. Color alone does not establish that the material is gold.
銀色に塗りました。 means painting something silver. It does not mean converting the object into silver metal.
Is 金色の箱 necessarily a box made of gold?
Show the answer and why
No. It states a gold-colored appearance. The material requires separate information.