Hi Solo,
Yes, that's right, the yellow ring is the result of yoni mudra practice. But not only that, it will begin to occur as you progress, during your meditation without performing yoni mudra. It will begin to occur during your every day life, to a muted extent when you just close your eyes. It will be visible when first awakening from sleep. Why? Because that is a reality of Anahata and of Ajna consciousness. So that you are experiencing a phenomenon that is a signal, a sign, that you are going in the right direction in your practices and lifestyle. I agree with Shanti that dwelling on this phenomenon is pointless. But on the other hand, you are enlarging the nadis and encouraging the psychoneurological transformation and development of your energetic system by this mudra. My Buddhist teacher told me that in his Theravedin tradition, this is said to be Anahata, the chakra of the heart. It is seen by some yogins.
Other measures that will enhance this perception and also serve to thus dilate the nadis towards transformational development, is preceeding the yoni mudra by dynamic chin pump while squatting, and preceeding that with alternate nostril breathing. Then standing and doing the yoni mudra while standing. And especially by pressing your chest up against a wall while standing. These practices will all enhance the golden ring. Later, the gold ring will progress into a golden shaft or pillar of light, and from that, into a full visual field golden light. Observe these effects with eyes open while in a darkened room, while facing east, up against a wall upon you can push your chest.
Mid-day yoni mudra and the other mudras mentioned above, will result in a varient on the gold ring. It will manifest as first a field of variously colored stars, and then develop into a yellow disc as bright as the sun, instead of the ring effect.
Ultimately, I believe the significance of these visual phenomena are the product of moving energy into the Anahata and Ajna chakras, past a constriction that is beginning to loosen. So the visual effects are merely a good sign. Whether the yogin exits his physical body at the time of physical death THROUGH the center of the yellow ring, is perhaps a hunch though this idea is somewhat confirmed as a basic concept in the yogic literature.
Just a few observations not within the purview of the lessons and teachings presented on this website by administrators.
x.j.