They all have a fiber reinforced polymer casing with a stainless steel bezel. The difference is that the slate model has a coating that makes the stainless bezel the slate color.
Because the back of the casing where is the charging port is stainless steel, the rest is fiber-reinforced polymer (plastic) and the bezel is also stainless steel. Seems pretty clear from the photos.
They all have a fiber reinforced polymer casing with a stainless steel bezel as mentioned above and its simply the coating on the slate that is different First picture is the back of the slate 2nd picture is the slate on the wrist 3rd picture is the stainless steel (cheaper model) 4th is the side of the silver model.
I think Garmin twitter need to check the specs, both devices are made of the same material and both the same weight. I totally agree about the wording should be clear. When I played with the slate grey I could not tell if the bezel was made or stainless steel or fibre
But take it from someone that has had both version in my hand, the models are the same apart from the colour. Whilst I didn't get the scales out, they are the same in terms of weight.
Regardless of this misunderstanding, the Vivoactive is a nice watch and in my view people will love it