Players don't spend Fate points to create aspects.
doppelgreener suggested what the player was trying to do is declare a story detail, however nothing in that section says it creates an aspect. Story details are just that, a detail about the story you're telling together.
Invoking for story details is only needed when it's a stretch of the imagination to suggest that an aspect (which is being invoked, and inherently true in and of itself,) means that something it's not explicitly stating. You don't spend Fate points to spin extra detail out of whole cloth.
Just because Aspects are true doesn't mean all true things are automatically aspects. To borrow from The Book of Hanz
-an aspect is something that gets camera focus in describing the scene.
To put it another way, there's a difference between a scene being dark, and a scene being Dark. A dark scene may be a poorly lit bar -but the lighting is just ambience. [sic] It doesn't influence the plot in any way. It doesn't really impact how the characters do things. It's just there to set a mood.
A Dark scene is different. In a Dark scene, we can expect somebody to jump out of the shadows at some point, or disappear into them.
What your player is attempting is called Creating and Discovering New Aspects In Play. In particular:
If you’re not looking for a free invocation, and you just think it’d make sense if there were a particular situation aspect in play, you don’t need to roll the dice or anything to make new aspects—just suggest them, and if the group thinks they’re interesting, write them down.
If your group decides "Hard to see up here" makes sense as an aspect, it is one. No additional mechanics required. However, a player will still need to spend a Fate point to invoke it as normal.
There's no need to create a new aspect anyway.
Now, from what I gather he can still attack- because he didn't do the "Create Advantage" action, instead he discovered an aspect that's logical on a scene with "Dark and Stormy" on it.
Since there's already a "Dark and Stormy" aspect on this scene, the player can just invoke that. Aspects are meant to encompass various details and don't need to be broken up into bits and pieces to be functional. Just as there would be no need to create another aspect for "It's Pretty Windy Out Here Too." If the scene is "Dark and Stormy", it implies we can expect somebody to jump out of the shadows at some point.
Consider an alternative.
If allowing players to invoke "Dark and Stormy" to mean it's hard to see an attack coming seems like a stretch, consider implementing Scaled Invocations.
With Scaled Invocations the relevance of the aspect is important. A relevant invocation works in the standard way. A tenuous invocation is a big stretch and you can only use it for a reroll. A perfect invocation is exactly what it sounds like and you automatically succeed with no roll needed.
If you're new to Fate I'd probably recommend minimal fiddling with dials until you get used to them but it may be the best option depending on the group.
