So far as I recall myself, the iconic is dark recess with golden highlights, but thats for Inquisitors in general.
It depends I feel, on how you feel your inquisitor does buisness. Are they open and ardent, striding through the middle of the battlefield, a shining paragon of faith in the Empero, meteing out His Justice as you go. Or do they prefer to be caustious, not advertise thier presence and paint thier armour red so thier own, and the enemies blood, doesnt show too easily. Or perhaps the colour of the armour indicates where it was made and by whom, Mechanicus Red with cog-esque scroll work to the trim.
Artifacts and embellishments though, can be done as you want. Are the skulls actual skulls, or cast in electrum. Would they be painted to be highlighted and spur fear in the hearts of your enemies, or to disguise mechanisms or features of the armour.
Sorry if this throws a spanner in the works!