I've noticed that the Targaryens all wear the same black-red color palette in episode 4.
The Targaryen sigil is a red dragon on black background, so I think red is being used to indicate how much of a "dragon" each Targaryens is.
Daeron = entirely in black
Daeron wants nothing to do with any of this. He is plagued by dragon dreams, but they are utter torture. Just give him some wine and let him take a mud nap without any prophecies involved for once.
Baelor = mostly black, with the smallest of red lining and accents visible
Baelor is the best of the Targaryens—kind, thoughtful, measured—but you don't want to forget that a dragon still lurks beneath. He just keeps everything very well contained.
Maekar = black doublet with large red accents
Maekar is hot-tempered, gruff, and grumpy. Doesn't mince words and far more uncontained than Baelor. He's not cruel like Aerion, but you certainly don't want to be anywhere near him or his mace if you piss him off.
Aerion = entirely red doublet
Aerion thinks he is a dragon in human form. He is erratic, violent, and cruel. He dies by drinking wildfire, thinking it will turn him into a dragon. Ergo, 100% dragon for him.
Egg's is the most interesting, visually:
Egg 1.0 = black doublet with large red accents
Egg is initially dressed very similarly to his father, which makes thematic sense. He's finally been brought back to his family, and Maekar has dressed him like his Mini Me.
Egg 2.0 = mostly all-black, with some small amount red stitching and buttons
He then changes into a nearly all-black outfit, with only the tiniest of red threading, which more closely mirrors Baelor. And look at that ^ face! That is a boy in awe of his Uncle Baelor for standing up for Dunk and doing the right thing.
Just a very clever bit of character work via costuming!
