Answer:
B. iris
Step-by-step explanation:
Eye color is produced due to melanin pigmentation in iris and light scattering by iris's stroma. It is a polygenic character i.e. it is controlled by multiple genes. Melanin pigment in iris can range from light brown to black. Colors like blue, green or hazel are produced due to Tyndall scattering of light by stroma. There are no blue or green pigments in iris.
Eye color can also change with age. Many European new born babies are born with light colored eyes. As they grow, melanocytes in iris start to produce the melanin pigment which can lead to color change. Puberty, pregnancy and serious trauma can also lead to iris color change.