It does happen in agriculture naturally. Unfortunately, the GMOs will spread to the native plants and then those will disappear. GMOs are a good idea; however, there are a lot of negatives to them. I just did a paper on them for my biology class. My professor seems to love things of that nature. Anyways...It could hurt the economy, on top of destroying native plants.
The color of your eyes is based upon the genes that you receive from your parents. You cannot control these; therefore, the ability to control what colors you get and then manipulate those colors is impossible. You would need to get contacts, but you made it clear that they do not want to get contacts. Other than that, I do not think it is possible to change your color. It does it naturally, though.