Flash Headshot

So let me start off by saying I don't do any of my photography "professionally". This is my hobby and a way for me to relax. However, recently my church reached out to me asking me to help them get some staff head shots. I have used my YN560 IVs for flash head shots (just to learn) exactly two times prior to this.

I'm looking for some feedback on the editing and lighting. This is not a real subject, just a buddy I grabbed from the church office to stand in while I tested out the setup. They want a grey backdrop and some staff headshots that look "churchy". They wanted them to be a bit artistic, creative, and somewhat candid. So I have Jay kind of laughing in this photo a bit as I'm trying to try this all out.

What I see, green. Is it his shirt? They gray background looks green to me for some reason. I also can't tell if I got the exposure right. Maybe my eyes are playing tricks on me. Please add feedback.

IMAGE LINK: https://flic.kr/p/FtNk​cK

It looks a little dark to me. The gray background is right on. Near his ear, it's RGB 79, 79, 79, sampled with the 5X5 average eyedropper in PS.

So question then, is there a way to "measure" and identify what the correct exposure is? Much like you did with the grey area?

Taylor02GT wrote in post #17977436
So question then, is there a way to "measure" and identify what the correct exposure is? Much like you did with the grey area?

Gray or white card? Or, I use this before I shoot: Need an exposure crutch?