sexing zebra bar gobies

[phantomtiger]

does anyone know how to tell the difference in male/female bar gobies? i have a pair in my 46 gallon mini reef. the larger one often flashes his colors more than the small one (his head actually turns a bright blue with black by the mouth), also this whisker like object comes out of the bottom of his head by his mouth. the smaller one does flash brighter colors sometimes, but not nearly as often. i have always assumed the larger one was the male but i really wish i could know for sure. i've searched the internet and have come up empty handed. they are for sure my favorite fish in the tank. they have a burrow which they protect together but i have yet to see eggs. the larger one also has a darker spot in his belly so i wonder if these are eggs? any advice appreciated, if curious what is in my tank go to my profile. i am new to this site. thanks, tabitha.