The fabric/colour used per Ladysewforus is the same that the real fett one (on my vest so). It's called Tackle Twill with a Greysh colour.
Your vest looks more an off white / natural cotton colour IMO :facepalm If your vest is made by Bobamaker, it's an off white cotton, because tackle is hard to get and he does it with cotton, not tackle.
But, please, BM does a high quality parts, don't misunderstand me.