What does the the pigs wearing green ribbons represent in animal farm?

Pigs started wearing green ribbons on their tails on Sundays it was for the rejection of animalism.

The pigs wearing the green ribbons in Animal farm represent/symbolize the rejection of the principles in animalism. They did exactly what Old Major warned not to do which was wear clothes, trade or earn money, etc. This also meant that they found the other animals beneath them and that equality did not resonate with them. The ribbons can also serve as a symbol of the pigs dominance over the other animals.