Erinhue's ring is Mythweaver, Air Ring of the Wordsmith. It's stone is a small chip of limestone , same as the Blarney Stone, which seemed very appropriate for a bard.
It is a Ring of Power ( from theTORC Guild) and it's main power is its ability to carry or transfer the feelings, emotions projected by its wearer and project them outward to those who listen. It is, in part (a small part the Bard would say) responsible for Erinhue's reputation of being Middle Earth's Most Famous Bard, mainly proclaimed by him.
Mythweaver is an Air Ring of Power and as such there could be a trick or three within its white gold band....like glowing green in the presence of lost items of power.