eye color is determined by pigments within the eye. eumelanin is dark brown to black and phaeomelanin is yellow to red
lots of eumelanin = brown eyes. no eumelanin and no phaeomelanin = blue eyes. lots of phaeomelanin and no eumelanin = hazel eyes. small amount of phaeomelanin and no eumelanin = green eyes.
if you delete or cut out part of the DNA, then you damage it. Depending on what is in the missing DNA, one may lose some genes or something else may happen. Not all of our DNA code for genes. Many DNA sequences have functions that we may not know of. If genes that produce pigments are cut out, then the pigments won't be produced, and a person may end up with green or blue eyes. There is no blue pigment. The blue color is produced by molecules in the eye scattering blue light, in much the same way that the molecules in the atmosphere scatter blue light to make the sky look blue. Scientists call this sort of coloration structural color since it is the result of the molecular structure of the chemicals that result in the scattering of blue light.
Cutting off DNA can also cause mutations, and mutations in the worst case can result in cancer.