Using Arnold, it’s extremely easy to add colour variations to particle/ MASH instances. This works in a similar way to the MASH Colour node, which is only available when using MASH in Repro mode (when the output is a mesh). When you’re working with instances, the job of colour variations is down to the renderer.
Here’s how the workflow works in Arnold:
You should now see colour variation across your spheres when you render the scene (remember to add a light!).