On: All the balls are the same color: brown

[drwl]

I would imagine it has to do with the retina where photoreceptors exist

/e all of the physical stuff has to do with magnification of the image (or incoming light) onto the retina

[AlbertoGP → drwl]

Yes, if you make the image big enough, looking at each ball individually it look brown, but the ones in the periphery take on their different colours.