Other brown layers will not work, they'll just create normal green laying Easter Eggers. I find a common, rising belief lately is that any brown layer x blue/green layer = olive egger. Originally the term Olive Egger came from crossing DARK brown layers with blue/green layers and continuing from there with whatever path you choose but preferably not back to the blue/green layer.
Also Cuckoos won't work too well, as their eggs are often poor in color unless you got some nice/rare dark laying lines.
