The rule of what players will remember about your scene-setting descriptions is that they'll forget game-important clues, while they'll remember unimportant details that have no real bearing on the story, but contradict other unimportant details (that they have, of course, remembered).
Strangely enough, if you try to conceal important plot information in apparently unimportant details, those will instantly be forgotten. Players have a sixth sense about these things.
So the trick is to supply a plethora of unimportant details, and then when players focus on some tiny thing that no sane person would notice or refer to ever again, you turn it into an important plot point.
Commentary by Keybounce (who has not seen the movie)
[Keybounce's comments will appear here when received.]
Commentary by memnarch (who has not seen the movie)
Dark blue is still blue! Admittedly that still wouldn't fit the scenes shown so far, but it'd totally be almost plausible on its own. I'm definitely getting some "patch the plot holes" vibes from this comic though. And from what I can tell, this seems so much better than whatever was originally in the movie. Seriously! This is top of the line shock and awe stuff; what better way to project strength over a planet than to shine a new sun behind your fleets? On top of being hard to counterattack against the light, everyone still on the ground would get a huge sense of dread as the sudden sunset heralds the invasion!
In-game, the GM here probably didn't think things completely through with their description and just went for a dramatic description. While they immediately confirmed Sally's great answer, alternatively, the GM could have played coy and neither confirmed nor denied it. At least for the moment. It would seem sort of like a magic trick for the players; what they see obviously can't be real, yet here it is still happening before their [characters'] eyes. Of course, Sally and Ben still have bad guy characters so they'd get knowledge about the trick later, but ideally the secret would get spilled after the Team Bad Guy players get to use it once themselves.
GM: Attacking PIEs are silhouetted dramatically against the red light of the setting sun.
Rey: You said the sky was blue just a few seconds ago.
GM: Well... there’s also a sunset.
Yanni: Is Takodana like Tatooine?
GM: Not in the slightest. Why?
Yanni: Without at least two suns a red sunset won’t be azure at the zenith. A zodiacal syzygy would be even better.
Darth Kanata: Maybe Galen Erso invented a way to project a sunset onto the sky, to make military invasions more impressive.
GM: Actually, you know what? That’s exactly what it is.
Chewbacca: That Galen Erso is a little scary sometimes. Brilliant, but scary.
GM: Much like all of you.