We will learn everything there is to know about the Metallic Material, including reflection index modes, Specular Map, IOR Mode, and much more.

Refractive Index Website. https://refractiveindex.info/?shelf=3d&book=metals&page=gold

#1 Lite is made up of wave lengths, 650mn is Red, 550nm is Green, and 450nm is Blue. The same colors can also be shown in another value called µm. To save you time converting nm to µm, here are the RGB color values in µm.
.65µm Red, .55µm Green, .45µm Blue.

#2 Under the IOR Mode, the left slider is the N (Refractive Index) slider, and the right one is the K (Extinction coefficient) Slider.

#3 Specular map must be turned down for the Diffuse channel or Sheen Layer to show up.

Note: There is a series of free 100% physically accurate Metallic Materials that you can download under the Asset Files section.