well, actually I would not consider it all that impossible as others are saying. It just depends on your setup. you need to change the environment to make your task easy
a) tracking
say you have a white surface, and three different fruits with distinct colors. You mount a webcam on the ceiling, looking straight down. You track the centers of the colors.
b) gripping & cutting
think of it as an x/y plotter: (something like this: http://makerbot-blog.s3.amazonaws.com/wp-content/uploads/2012/03/nyc1591-650x437.jpg)
the "arm" consists of a gripper with an integrated knife, mounted on a linear bearing system for movement in the x axis, and a linear actuator for movement in the y axis.
you put 3 fruits on the table, which all have similar size (fit for the gripper) and different colors. You want to cut the red apple? The software on the computer finds the centre of the red blob from the webcam feed. The "arm" moves its x position to the blobs x position. The "arm" expands until the linear actuator has positions the gripping element on the blobs y position. Then the gripping element carefully closes. The cutting element cuts it in two pieces. Then the whole thing retracts and voila.
And yes. you can do that with roborealm and arduino.
And no. even what I suggest will not be easy.