The PxrVary pattern allows for random variation. Let's try varying the color of the teacups based on the Particle ID.
Select the nParticleShape1 node. Look under the Instancer attributes. Change the Object Index from None to Particle ID.
This causes a primvar called particleId to be available on the instances.
Next, wire a PxrVary pattern into the color of the material used for each of the cup and the saucer.
Set up the PxrVary to use the particleId as its seed for randomization.
Now the render looks like this: