By any chance do you know what the grayish rectangular ring on the back of the slate titanium is. It separates the front part of the case with the back part of the watch? I’ve seen it with the natural and gold titanium as well. But the jet black doesn’t seem to have it. It’s all one piece to the back.
Jet Black is full body without that line “separator” to give it a special aesthetic look. I think Apple took a lot of Pride in this Jet Black version especially it being a come back that was very beloved in iPhone 7.
Also Jet Black is a deep true black that a “separator” doesn’t really make sense with it. As it would be a true black on black which would cancel each other out unless it would be a different type of material to create differential. All of that just doesn’t make sense design wise.
Natural, Gold and Slate Titanium having that line separator is as well pure aesthetics.
To me they both look nice in their own way.