I've no idea where this grey is coming from. Transmission 1.0 and Roughness 0
I found a fix! Apparently my normals were facing the wrong way. You can check this by clicking on overlays and checking "Face Orientation"; Red means it is reversed. I Selected all my vertices and hit shift-n and voila no more silvery things! Thank you everyone who gave suggestions.
I believe it is reflecting the world texture. Try changing the color of the world as represented below and see if the reflection of the cup remains grey.
Another suggestion, change the IOR of your glass texture. This is related to the degree of the glass, like the ones we use in the face. Try putting it into 1 and it will show the object inside without any distortion.