A tinge? A TINGE? This moment is like romanticus maximus. It's incredible. It's twisted, sick, broken and wrong but dammnit, it's also EPIC. It's Hellenic. It's a moment that absolutely captures that ugly, selfish, greedy aspect of love that is always there in some way... you know they say if you love something set it free... the Joker will never ever set Harley free, his love for her is all about his own self-gratification. Haven't we all struggled with that at some point in our lives? Even here, he must entrap her in a permanent state for his own admiration and reflection rather than allow her either to be freed through death or included entirely in his life and vision.
Yet there is something very, very tender and even sorrowful in it. He does it because he's a monster, he can't compromise on that. But he loves her too and so he wants her in some fixed aspect for him for always. There's awareness of the pain he's caused her and awareness of the way he's cheated her. He isn't remorseful about it, but there's something of longing and loneliness in his face in those final panels. In confessing to her something so intimate about why he has chosen to do what he does, he also distinguishes her very significantly.