that's what I was thinking too bd.. Why on earth would PLAN paint the outlines of the opening almost the same color as the flight deck? it doesn't make any sense to me.
You want to make it VERY VISIBLE so that some poor sailor is not accidently standing on top of it or park a vehicle/plane etc over it when some poor sap wants to bring some missiles or bombs up to the flight deck!
Every single marking, lines etc on the flight deck serves a purpose and that is safety because it is quite dangerous on the flight deck and visual cues are crucial since you can't hear anything! There is a reason why on carriers every line is painted bright colors like white, yellow, red so nobody stands on the wrong spot and gets injured or killed!