Yep.. It might have been exactly like you said. Here is enlarged piece of the first picture posted above. If there would be a silver or yellow ring there it could be noticed . Especially that the yellow number 12 and bar are well seen while the front ring is dark. We can argue about the yellow underside of the engine cowling. However the second picture of its front area shows dark paint there comparing to the one on the wing undersides. Taking the kind of a negative used for picture taking into consideration it might be possible it was yellow. So the ring wasn't yellow because it would be as dark as the number 12. Also we can compare it to the lower part of the absorber of the landing leg. For sure it is of bare metal ( silver ) because the part wasn't painted at all.