Looks like a duck egg to me. My Scovies lay that off color whitish green. They feel very waxy though. Like they are covered in crayon.
Do a comparision touch. Rub both the brown and poss. duck egg and see if one feels waxier. Also, the duck eggs get bigger quicker. My ducks eggs went fm smallish, for a duck egg, to large in just a matter of 3-5 eggs laid. My pullets usually take a few weeks to size up to large.
