Is it possible to change eye colors without contacts or corneal surgery?

Not safely. There is at least one person in another country that I have heard of who puts in iris implants for purely cosmetic reasons, but there a lot of complications associated with this.
Not really. The iris, behind the cornea, determines the color of your eye. There are some drops used to treat glaucoma that can change green eyes slightly more brown.
No. Eye color is the color of the iris, which is inside the eye, behind the clear cornea. The color cannot be changed, but colored contact lenses or colored implants (for patients missing portions or the iris) can make the eyes appear a different color.

Related Questions

Please explain if it is possible to change eye colors with-out contacts or corneal surgery?

Yes. Certain eye drops can cause permanent darkening of the eyes, but they are rarely, if ever, prescribed for this purpose. Colored contacts are the easiest way to change the appearance of your eyes. Read more...