The front of drywall is usually gray, blue, green, or purple and will have a nice and smooth surface for finishing. You will also notice that it is somewhat tapered on the long edges of the drywall.
The first giveaway that you are looking at the back of the drywall is the paper on the front is folded over the edges and glued to the rear. The folding helps reinforce the gypsum core and protect it. The other dead giveaway is the brown color. Although some companies use gray, brown is more common.
- Gray Drywall: Finish Side Is Gray - Green Drywall: Finish Side Is Green - Purple Drywall: Finish Side Is Purple - Yellow Drywall: Finish Side Is Gray