The posterior portion of the vascular tunic is pigmented due to the presence of pigment producing cells called

Answer is choroid.

Explanation:

The vascular tunic is considered to be the middle layer of the eyeball, which comprised of three parts namely, ciliary body, choroid and Iris.

The choroid is located or found between the retina and the sclera. It is pigmented and contains melanocytes. This appears dark brown because of melanin. The melanin present, absorbs stray light rays, preventing scattering and reflection.