Both techniques have advantages, the vertex tag version would be better suited to a ‘hero’ object close to camera that is deforming as the colour would be stuck to vertices.
The spherical gradient version is just remapping a 3d gradient based on distance so if the ‘stalks’ were animated they would swim through the colour and it wouldn’t be fixed to the surface. It’s good to have both methods in the armoury.
I’m really pleased to have helped, I cannot take the credit I learned it from a generous Blender user. I don’t know who it was but as soon as I read your question I knew how to do it. So some of the gazillion Blender tutorials I’ve watched have actually sunk in. Glad to act as a conduit in this case.
This last month of watching the amazing #nodevember creations on Twitter has taught me that literally anything is possible with Cycles, genius level users are able to create a 3d field of sunflowers on a single plane or a fully animated animated robot with laser spitting eyes from one cube by the power of Cycles nodes. I have new found respect for Cycles and a wish to dig much deeper because it’s an absolute goldmine.