Eye color does not actually change with mood. What does change is the way light reflects off the iris, creating the impression....
Eye color is a polygenic phenotypic character determined by two distinct factors: the pigmentation of the eye's iris and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.
In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma. The appearance of blue and green, as well as hazel eyes, results from the Rayleigh scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky. Neither blue nor green pigments are ever present in the human iris or ocular fluid. Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.
In linguistics, grammatical mood is a grammatical (and specifically, morphological) feature of verbs, used to signal modality.:p.181; That is, it is the use of verbal inflections that allow speakers to express their attitude toward what they are saying (for example, whether it is intended as a statement of fact, of desire, of command, etc.). Less commonly, the term is used more broadly to allow for the syntactic expression of modality — that is, the use of non-inflectional phrases.
Mood is distinct from grammatical tense or grammatical aspect, although the same word patterns are used to express more than one of these meanings at the same time in many languages, including English and most other modern Indo-European languages. (See tense–aspect–mood for a discussion of this.)
The equine eye is the largest of any land mammal. Its visual abilities are directly related to the animal's behavior and the fact that the horse is a flight animal. Both the strengths and weaknesses of the horse's visual abilities should be taken into consideration when training the animal, as an understanding of the horse's eye can help to discover why the animal behaves the way it does in various situations.
The equine eye includes the eyeball and the surrounding muscles and structures around the eyeball, termed the adnexa.