What is an example of mutation that could cause a phenotype that makes organism better suited for its environment?

Explanation:

If a mutation led to brighter feather colouring in birds, the brighter feathers may allow those individuals with the mutation to reproduce more frequently, because they are seen as being more attractive and a desirable mate.

answer; ///i believe the correct answer is (aids) acquired immune deficiency syndrome;

allowed for the prediction of the properties of missing elements.