When you put a crafting material on the main/primary slot on your armor, it not only dictates the rating for your armor but also dictates the color of your armor.
When you put a metal material on the primary slot, it changes the color of the “metallic” parts of the armor. Same goes for leather and cloth materials. However, do note that not all “parts” on the armor will change color.
Note that Fade-Touch materials can override the colors of certain parts of the armor when you select one.
Below will point you to the gallery of what colors each crafting material gives.
For cloth material colors click image below to see the gallery:
For leather material colors, click the image below to see the gallery:
For metal material colors, click the image below to see the gallery: