Dr Spencer's eyes are only visible when he's saying the name of a drug. Aronofsky points this out as deliberate in the commentary track.
The only time we see Marion in red is inside Harry's visions. The only other character that's associated with that color is Sara (her obsession with fitting into her red dress). It's heavily implied that in Harry's mind, he sees his mother in Marion, despite the fact that the two are nothing alike in personality, which is one more example of how flawed their relationship is.
Darren Aronofsky has stated that Tyrone is the only character capable of reclaiming their life, and this is subtly shown in the “fetal position” scene and the “hope” each character has at the lowest moments of their lives. With Harry, there is no hope for him. With Marion, her only hope is her addiction. With Sara, her only hope is escaping reality. And with Tyrone, his only hope is the memory of his mother. Unlike the other three, Tyrone’s “hope” is the only hope that is any form of positive reinforcement. The warm memory of his mother will help Tyrone endure prison and heroin withdrawal, and the memory of his mother may ultimately help Tyrone stay clean when he gets out of prison.
