I sent sims to the consignment stores a few times. One of them got an Invention Gnome at the consignment register in the garden shop of my Carter's Cnr Store.
Another got a miner at the Elixer register in the Magic Shop at Carter's Cnr Store. Another got a miner at the Elixer Consignment Store.
They consigned and purchased a few other things too.
Then my nectar expert got a ghost gnome from the Claw machine.
I played with it for a while by ageing it up and down. It starts out pink. When I made it changed colour when I made it a child, then changed again when I made it a young adult. It didn't change colour when I made it and adult. It did change to purple when I made it an elder.
Then I aged it back down again to toddler pink.
I assume the different colours we see for the ghost gnome represent the various ages it is. So when it turns purple it is probably time to turn testing cheats enabled on and set its age back to toddler - unless you want another gnome tombstone to decorate with.