Hi Kent-
Here is a Material Graph setup for a layered material that will achieve the desired "aura" effect on a plane below a water (Liquid material) surface. Create a simple white to transparent square gradient in Photoshop, and save it as a PNG with transparency. Then, plug the gradient texture > (Source) of a Color Invert node > (Transparency) of a Toon material. Set the Toon Color to the desired "aura" color, set the Contour Width to zero, and uncheck all the Advanced options. This is the base Surface material. Add an Emissive material as a Label on the Toon material. Plug the gradient texture > (Opacity) of the Emissive material, set the Color to the same "aura" color as the Toon material, and uncheck all Advanced options except for "Visible in Reflections" and "Two-sided". This will also work with the Scattering Medium- just enable "Visible to Camera" in the Emissive options. Note that this setup must be rendered in Product mode; it doesn't work with Interior mode. Example render and matGraphs below.
Cheers,
Eric