I have a set of geometries that they're generated by "Instance on points" Now i need to set a Color Ramp attribute for these geos to set a rainbow like material to these geos In fact, i need make an attribute for these geos to set a different color (by color ramp) to every geometry
For instanced geometry, you can use
Random value from
Object Info node in the shader editor.
If you want to realize instances or do it from geometry nodes, This setup lets you create random color per object using color ramp.
Attribute input of last
Transfer Attribute node with
Random Value for randomization.
Note that it only works if all objects have same number of vertices.
There is a better solution to this problem by Robin Betts idea of scaling instances to 0 and transferring attribute. Which even works with objects having different number of vertices.