Peter Parker first swung into the Marvel Cinematic Universe in 2016's Captain America: Civil War, but it was the following year that the wall-crawler was properly reintroduced in Spider-Man: Homecoming. Looking to capitalise on their newfound relationship with Marvel Studios, Sony Pictures added heaps of MCU references to that movie, including some big cameos.
Chris Evans showed up as Captain America, while Robert Downey Jr. played a supporting role as Iron Man, though his armour only underwent a few superficial changes rather than the normal redesign between movies. Now, we know why Tony Stark's suit ended up with a new colour scheme clearly inspired by Iron Man's appearance in The Ultimates comic books.
"Those with a keen eye will realize this model is just a recolour of my Mk XLVI from [Captain America: Civil War]," concept artist Phil Saunders explains in the Instagram post below. "Sony didn’t have the VFX budget for a whole new suit, so Kevin Feige requested a nod to the Ultimate Iron Man in the repaint. And after a few variations, the Mk XLVII was born."
It's interesting to hear that Sony Pictures didn't have room in the budget to give Iron Man an overhaul, but it clearly wasn't a major priority for the studio. Just the Avenger's presence in Spider-Man: Homecoming had the desired effect on box office takings, and a new armour wouldn't have changed that (switching up the colour no doubt sold a lot more toys on Disney's end, though).
Check out this amazing new concept art from the 2017 release below: