It Gets Complicated

 Plasticity is the ability of your genotype to change the phenotype of the organism in response to environmental changes. In order to test if the trait you are testing is plastic you could put your organism in different environments that would encourage your organism's phenotype to change. Take this butterfly for example, during the dry season it has spots on its wings to scare off predators, while in the dry season, it changes to a brown color to blend in with the fallen leaves and dry foliage to avoid predators.