Phase mimicking?

Would water vapor compressed without undergoing phase change to the density of liquid water possess the same characteristics? As in, besides the high temperature required to maintain the gaseous phase under high pressure, would you be able to tell the difference? What if you could sustain gaseous water at the same density as liquid water at room temperature?

Naturally there will be some differences, like how it would fill up every portion of the container due to the pressure, but would it look like liquid water if you had a very large tank of it? Would it appear blue?

I'm trying to reconcile with the differences between the gas and liquid phase of materials.

Another question...do all liquids boil in a vacuum? I have only heard of water boiling, but not mercury or molten iron. I would assume they would boil...but maybe there is something I am missing.

Thanks.