Guineas lay a variety of colors. Their eggs can be white (Not fully white like chickens), brown, or tan. They might have spots or speckles. There may be a ring of speckles then a plain tan ring and then another ring of speckles. (I have a hen which lays eggs like this) The end of the guinea's egg is pointed. A guinea egg should be a little smaller than a medium chicken egg I'd say.
I assume guinea's are just like chickens to where each hen can lay a variety of each color. Either white, brown, or tan eggs. With spots or speckles or none.
I get mainly tan eggs with speckles. If you want I could post some pictures.