Believe it or not, the ending for Avengers: Infinity War was originally going to be even darker than it already is.
After Thanos snaps his Infinity Gauntlet-ed fingers and wipes out half of all life in the universe, he ends up in a sort of limbo (thought to take place inside the Soul Stone) with a young Gamora, who asks him, "Did you do it?" When he responds in the affirmative, Gamora asks, "What did it cost?" Thanos's response: "Everything."
An early idea for this sequence had the Mad Titan walking on a river a blood that would represent the countless victims he'd simply snapped out of existence. While speaking to /Film, Visual Effects Supervisor Dan Deleeuw admitted that the blood concept was just "a bit dark."
Kelly Port, senior visual effects supervisor at Digital Domain, who described this realm as a "way station," said that there was a lot of time spent on what it would actually look like.
"We went through sort of an exploratory phase with that one, so looking at different options, and what does that mean, and talking a lot about that. So that went through some changes."