It gets complicated.

 Plasticity is when a single genotype produces more than one phenotype. You would typically see a plastic trait when things (like the environment) change often to select for it.

In order to determine if a trait is plastic you could take the organism out of its natural environment and study it in a new environment to see if that trait changes or stays the same over time. If the trait changes then it is plastic, like the lizards we learned about in class. On the lava flow the lizards were black but when taken out of that environment and placed in a sandy area then over time the lizards would turn brown.