hmmmm...not real clear on what results you are really looking for, but here's my two cents.
Is the tank going to have a black base and then silver flake or metal flake base covering the whole surface area?
There's two options that come to mind. A dry blue pearl added over the silver using intercoat clear. This will give you a hint of blue and will be noticable at angles more than the direct angle you are looking at it.
Another option that comes to mind is tinting intercoat clear with oriental blue or cobalt kandy koncentrates (blue tint in your paint line will work). The color change will be over all and more intense as you build up layers. Remembering not to get too thick with intercoat clear.
MY BIGGEST advice is to find a spare part or surface area to try out the different ways before starting on the tank.
I'm not real clear on the results that you are looking for, but I hope this helps!