The color of gunmetal will give you varying results based on the lighting you are using. Most of ESB and ROTJ Vader was shot against a black floor. The result is that the gunmetal comes off as near-black. This Is one of the reasons you didn't notice the harlequin pattern. If you,are planning on using the screen accurate paint it will look very silver, similar to your first two photos unless you light it correctly. Many of us in the 501st paint a much darker gunmetal intentionally so that when viewed under more normalized lighting conditions and floor colors the gunmetal emulates the on screen appearance.
Food for thought.