I hadn't noticed that, only that my eyes go funny when examining the graphic closely. I have to blink and do a second take on it.
I should maybe say how it's done:
* One ring was drawn in Xara Xtreme and a bevel added.
* Three copies of the ring were made (4 total).
* Three rings were placed equidistant and made to look as if they interlock.
* The rings are joined into a group and then duplicated.
* The duplicate set of rings is made much smaller and placed exactly in the middle of the larger set of rings.
* An 11 step blend is made from the larger set of rings to the smaller set.
* The colour and size of the remaining bevelled ring is changed and put to the back of the others.
* Lastly, the frame is drawn and put to the back of everything.