The renderman/arnold/vray procedurals transfers all Each render engine procedural takes care of transferring the agent metadata to onto the meshes (all the metadatas names has a render meshes, this process adds an "atoms_ prefix during rendering). It is possible to " prefix to all metadata names. You can use these metadata inside shaders. This can give you more control on agents variation during renderingwithin shaders to have better control over your agent variations at render time.
For example instance, you can create an agent group and with an addMetadata module you can create a metadata called myColor. Use . In the addMetadata options set "myColor" as name for your metadata, the type to "vector" and then open the agent override dialog to set different value random values on some your agents.
Go back to your variation scene. Create a simple renderman pxrsurface shader and as diffuse color connect a pxrattribute node to the diffuse color. Set the "variable name" attribute of the pxrattribute node to "atoms_myColor" and set the type to vector3vector.
Now you can export Assign this material using the Renderman material exporter from the Atoms menu. And you can prepare an agent variation that use this shader. The you can render and you will see something like in to all your meshes and re-export the variations with the variation builder (make sure to select renderman as target render engine).
In your simulation scene, import your variations again and set the variations onto your agents. Once you render, you will see a render similar to the picture on the right, where the shader color is taken from the myColor metadata
(the addMetadata module should still be applied on your agent group and set up as explained above).
This can also be done also in arnold Arnold using the aiUserDataVector/Int/Float/... node or in vray V-Ray using a VrayUserColor node as well.