There's a target in my arrow; or rather, a pattern of alternating light and dark bands. Why?

I noticed while looking into the end of an aluminum arrow that there was a pattern of perhaps 6 concentric bands of bright yellow light (the color of the slightly translucent nock at the far end, through which the light presumably entered) alternating with black, fading to darkness towards the periphery. The bands were all of equal thickness, and remained circular and concentric if the arrow was tilted (although they became slightly blurry), ruling out any kind of interior markings. The interior seemed to have more of a matte than a mirror finish. My guess is that this is the result of wave interference, although I would have though this would require something close to a mirror finish. Anyways, I can’t find anything through google addressing this; any ideas?