In the sentence you provided, the linking verb is "is" (implied in the phrase "desert iguanas turn bright white").
The predicate noun is "white" (which describes the state of the desert iguanas, linking back to the subject), and it serves as a predicate adjective as well since it describes the condition of the iguanas.
So, in summary:
- Linking verb: is (implied)
- Predicate noun: None in this sentence
- Predicate adjective: bright white
The main focus here is on the predicate adjective ("bright white"), which describes the state of the iguanas.