Favorite Son - S1-E6
Revealing mistake: When Lucifer is going through the forensics bag next to the dead body at the start, the body of the victim can be seen breathing. (00:07:30)
St. Lucifer - S1-E11
Revealing mistake: When Chloe is getting dressed at the start of the episode, she is wearing a flesh colored bra underneath the bed covers that she has wrapped around her when she mentions her ex dumping her by text.
Favorite Son - S1-E6
Revealing mistake: When Lucifer takes off in Chloe's car during the stakeout, tyre marks are visible in the gravel from previous takes. (00:32:10)
Lucifer, Stay. Good Devil. - S1-E2
Revealing mistake: When Jimmy grabs the cell's door, in the shot that happens before he starts banging his head on it, the supposedly secure door gives way effortlessly, showing big gaps. (00:42:30)
Revealing mistake: When Lucifer convinces Ricky not to jump off the building, it is blatantly obvious that the two actors are on a green screen and not an actual rooftop. The green glow around their heads is visible. (00:13:10)
Answer: It's Lucifer's blood from when his wings got hit by the bullets. As Lucifer spreads his wings, they're white, and before he wraps them around Chloe, you see a bullet hit his wing above his right shoulder, and the spot turns red. After that, he continues to get shot in the wings before fleeing.
Bishop73
Agreed. His wings take damage and "bleed" similar to how he bleeds when Decker is around.
Ssiscool ★
If they were normal bird's wings, the lower part where there are just feathers should neither bleed like that nor be able to stop bullets, but they are angel's wings, so they behave differently.