I believe when they say marbled, they are talking about two colors in each eye, such as the eyes are marbled brown and gold or blue and brown. Not distinctly brown or distinctly blue.
Hi,
I raise fainters and have a lot of blue eyed goats in my heard. Marble eyes are eyes that are both blue with brown "marbled" in. Sometimes a baby will have blue eyes for several months and then their eyes will marble to a combination of both colors.
My buck BBB is somewhat marbled. His eyes are blue, but if you look really closely you can see brown around the edge of the iris. A couple of his blue eyed kids by him have also had this. In one it was thick enough that when in the dark, and her pupils dialated, her eyes looked brown...but in the sunlight her eyes were blue when the pupils were small.