FStormDistance texture calculates procedural 3d color gradient based on distance to select geometry surface.
Radius sets gradient width.

Radius can be controlled with an input texture.

Offset sets gradient shift toward the surface.

Invert option switches the gradint from outside to inside.

Double side option ignores surface normals directions and calculates the gradinet for both surfaces sides

FStormDistance texture can work with bump mapping.

It can be used for mixing different materials, other textures or in any other ways.