I had a devil of a time trying to photograph these necklaces. Glad I finally captured a few views to share.
It does look like an egg yolk. They are vintage Swarovski cabochons.
Those Millefiori hearts just make the necklace. Luckily, I purchased these when they were a $1 per strand (you had to buy 3 strands though.) Now one strand costs twice that.
Yellow millefiori hearts and royal blue Czech hearts, oh yes!
I purchased mine from MK Beads a couple of years ago.