Love thinking about Bianca, Nico, and Hazel's forms in sosf.
I like to imagine that Hazel's voice sometimes sounds like two at the same time, hers and Persephone. She wears a crown of gold-red blood roses. Sometimes her eyes shift to pure black like Pluto's. She has golden streaks in her hair and on her skin from the whole.. ordeal at the end of doo. Her clothes are a gold and red mix of colors. When she walks flowers appear beneath her and wither as she walks away.
Nico's eyes are mostly purely black, but often times they shift gold like Kronos'. His outfit is black and gold. His form continuously shifts between different ages, you'll think you're talking to a child but then he's an old man and then in his mid 30s. He rarely physically displaces himself and just teleports around, and his outline is always fuzzy and indistinct. Whenever he's around, you can faintly hear a clock ticking.
Bianca's hands and forearms are blood red and gold. Her eyes are dark red, and if you look carefully there seems to be like flickering flames in them. She has blood tear streaks down her face. She wears an upside down silver-black crown. She wears outfits that are a mix of clothes from especially chaotic or violent times of human history -- trojan archers' armor, maybe a pin from the French Revolution, bits and pieces of various war uniforms (belts, boots, etc).
he I just like to think they share colors... despite everything they're siblings. also I think it makes sense in-story?