Not oxygen unless they have changed paint codes. However, I think you are right, a gas bottle. Nitrogen or another inert gas at a guess but then again I don't know what helium or hydrogen bottles look like so I am guessing.
I saw the valve get knocked off of a full oxygen bottle, twice actually. The first one flew a bit over a hundred feet, hit and buckled an H-beam holding up a pipe rack about ten feet tall and started spinning on the concrete. It spun so fast that the center it was spinning on looked like a ball with everything else invisible! I didn't have a clock on it but I think it spun over a minute. Amazing how much more careful I got about keeping the caps on my personal bottles!
Hu