Mustard gas should have a blue body, yellow fins with a butterfly stripe all the way around it's fins so technically it's a type of butterfly. Most of the mustard gases on AquaBid right now are not true MG's and are just Bi-colors with blue bodies and yellowish fins. But as I said to be a true mustard gas they would need that band of blue around it's fins.
My boy in my avatar is a true MG.
So are you talking about a blue bodied fish with yellow/orange fins with a white outline? If so that's just a Butterfly, not MG
Still beautiful though.