How to use gradient on flat surface?

Hi and welcome to this forum!
Please, have a look at this post:

it is really useful…


That said.
You can’t make gradients with surfaces, but you can color mesh vertices.

In your case a single triangular mesh face will be plenty.
Remapping vertices Y coordinate to a 0-1 domain and using Gradient component to get colors to feed on the mesh creation (1 color per vertex).


triangle gradient.gh (10.8 KB)