Gray on Bravo upper units

Looking at photos of a boat. What do you make of this gray on the upper units of the Bravo Drives?

 

Since you are running a shower cooling system, this is probably a high power installation. They may be overheating. Also, hot salt water is corrosive and that may also be the cause.

 

It's not my boat. I saw it on the internet and my first reaction was I don't like the look of that gray. Heat is what I thought too. Don't know if it's overheating or if that happens in some water and is normal. Notice no discoloration where the mercruiser logo is or below that. Engines are stock 502s. Has anybody seen drive showers discolor an upper like this before? I've seen mineral stains on a drive before. Those were more like defined streaks going from upper all the way down the sides.