Chase prepares to stick a needle through the patient, Addie's, right eye. This eye is very dark, appearing to be a very dark brown while Addie's left eye is light, appearing gray or light blue. She doesn't have different colored eyes, because her eyes were the same color in the first scene's fight. In preparation for the procedure they would have administered eyedrops to dilate the pupil to allow access for the needle without risking damage to the iris muscles, but this does not explain the color change.