These are not flashbulbs, merely incandescent A-lamps, but check out the sweet vintage ad!
So the “blue dot” thing was a quality indicator that Sylvania used in their classic flashbulbs. A magnesium filament inside an oxygen environment within the bulb produced a bright flash of light, assuming the envelope hadn’t been compromised. A dot of anhydrous cobalt (II) chloride inside that zero-moisture bulb would remain blue. If there was a leak, atmospheric moisture would react with the cobalt chloride to turn it pink, an indicator that this bulb might not work.
What’s less clear is how, exactly, one wee flashbulb is going to effectively illuminate that whale – flash photography being not super effective at distance – but whatever.