Can trauma change eye color

[Brimaze]

From reading articles about blunt trauma to the eyeball,they say that trauma can change the color of the iris ,how does this happen? Does the whole of the iris change a different color ,like blue to brown or vice versa? Does it turn the iris color darker or lighter? Is this something to do with the pigments?  

[John C Hagan III, MD, FACS, FAAO]

Several mechanisms can work. There can be trauma to iris and some of the pigment falls out making it lighter in color, The pupil might not work right (traumatic iridoplegia) making the color seem difference because the pupil is larger or small than the other one.  Or there can be scars on the cornea which make it look different in color.