The blue in Amy's bedroom was an idea of Adam Smith to show that it was inspired by the TARDIS from Amy's encounter with the Doctor when she was young.
The Doctor's gesture indicating Rory's long nose wasn't in the script. This two-parter was actually the first episodes filmed, before Arthur Darvill had acted on the show, but after he'd been cast. Matt Smith and Darvill were already old friends, so Smith already knew about Darvill's honker and improvised.
Steven Moffat came up with the concept for this two-parter when he was thinking of the worst possible situations to be in with the Weeping Angels and thought of the inability to see. His first idea was blindness, though this developed into the situation that Amy ends up in.
In 2020, Steven Moffat admitted that he should not have played the scene where Amy tries to seduce the Doctor "for laughs", noting that Amy ignoring the Doctor's protests against her overtures does, at the very least, have some rather uncomfortable sexual assault undertones. He admitted that this was the one thing about his era would change.
Matt Smith had difficulty saying: "the forest is full of angels", instead he said: "the angel is full of forests". There's even a t-shirt in existence showing the phrase.