Gas has a distinctive small. Open it and see. Obviously if you do smell gas, ventilate the room and wait for it to clear.
Yeah it’s not dangerous to just open it for a second to smell. The handle looks to be blue though, so i’d wager it’s more probable to be water and keep a bucket under it.
Never trust colors with piping or wiring, always assume it’s wrong and do proper tests.
I had some people install a new water heater at my place. They turned off what was labeled as the water heater at the breaker and proceeded to change out the heater.
I noticed later that it seemed odd that the AC hadn’t cycled on all day. Eventually realized the circuit breaker was mislabeled.
The guys doing the water heater replacement were working on a live line and I guess they didn’t bother to check with a multimeter. Jesus. They didn’t get hurt/killed thankfully.