Why do the iridescent colors seen in some seashells (such as abalone shells) change as the shells are viewed?

Question

from various positions?

Answer 1

It's mostly due to constructive and destructive interference effects, since the thickness of the platelets that make up the iridescent coating (nacre) is in the blue-green part of the visible spectrum, at about 500 nm. See the ref.

Answer 2

The colors are created by tiny crystals diffracting and refracting the light like little prisms. When you change the position of the shell the angle the light hits each crystal at changes and, just like turning a prism, the pattern of colored light changes.

Answer 3

because the light reflects deferently off of the seashell