Along with the matching bracelet, Kate debuted these extravagant and magnificent earrings at the St. Andrews Gala in NYC (December 2014).
Here is the closeup:
You can better see the yellow diamonds in the photo below.
The earrings are made of an emerald surrounded by white and *yellow diamonds in a square-cut setting. About three strands of white diamonds cascade down to the emerald pendant, creating a chandelier appearance. It looks like the two outer strands consist of small diamonds while the center strand features much larger diamonds. A post with a salient edge clips the earring on. The post is studded with white diamonds and appears to be an addition to the main component of the earring, probably added on after the pendant and strands were created.
It looks like all the diamonds are different shapes and sizes. I see baguettes, marquises, and round cut diamonds on this piece.
Like the bracelet, I believe this is set in either white gold or platinum.
*With thanks to Joyce P. and Anna of MSO for pointing out that there are light yellow diamonds on these and the bracelet as well.