The 7XI has average, matrix and spot metering. In the average mode, if the horse takes up the majority of the frame then you will a gray horse. Average meters assume that any subject is comprised of shades from Zone IX to 1 and averages out all the tones to 18% gray or zone V. In spot mode, what ever you meter spot is seeing will be exposed at zone V. I think the 7X1 it is about 3%, In Matrix metering, maybe, maybe not. If all the cells are reading the same tone, then you will get zone V, but if you are back a bit with some backlit, maybe the chip understand that you have a black object and will compensate for Zone III to I. It is best guess by the chip. Best bet is to use a gray card or the plam of your hand as the referance for you horse shot. Of understand that you are reading in Zone V, underexpose by 2 stops to zone III, the core of the Zone System.