Black Iridium has a darker color (therefore blocks out more light) and a mirror coating, while grey blocks out less light and does not have a mirror coating. The Orange Radars look to be Black Iridium but I can't confirm that.
If you are comparing Black Iridium and Grey, both use the same base but Black Iridium has the mirror coating which cuts down on light transmission significantly. Getting into Light Grey, Dark Grey and Warm Grey is another story but I don't believe any of these were made for the Radar so we'll skip that.
The bottom picture is definitely grey, you can see the temple piece as well as his eyes.
Ok then Grey it is! Gonna have an exact match of the one above Should work well to balance off the extremely attention-grabbing atomic orange frame. I could feel almost everyone's eyes on my radars when I was cycling at the park the other day