Silver Plate is a plating that matches the color of Sterling Silver. Surgical Steel does not match Sterling or Silver Plate well. Yellow is a bit brassier than Gold Plate but is usually a longer lasting finish, especially on clasps. Gold Plate is closer to the color of 14kt gold, but may not stay that way for long. Gunmetal is black nickel plating, which looks antiqued.
Copper is a soft, reddish-orangish metal.
Because it is soft, it is a nice metal to use for wire wrapping. However, it isn't very durable when made into light weight charms and other findings. We now carry a small line of copper plated findings and beads - inexpensive but fairly durable. Antiquing Solutions are a quick way to change the color of findings. Color Magic Stain is a permanent enamel-like paint coating, that is great for coloring charms and all metal findings.