Whats the best way to model interface between two liquids?

Hi! I am a beginner, and want to model liquid-liquid seperation using blender. I tried but I am struggling to model the iterfaces between two phases as shown in the above two figures. I request for your help.

I would use material not geometry for that, here is a simple way for this.
It can get fast complicated if you use seperate shaders, i would try the this solution with colorramps first.

material_cocktail.blend (837.9 KB)

thank you for taking your time to design this. I checked the render, its better than what I had tried earlier. Can we make this look more photo-realistic?

You can use transparency instead of alpha and tweak subsurface scatter. It will take a lot more cpu power and rendertime.
Take a look at how to tweak orange juice and milk:

thanks a lot!!