When you see Umbridge's office, what do you think it tells us about the old hag?
She's obsessed with pink, everything's pink, everything's cats, everything's doilies, it's all sickeningly cute, it's all fluffy and nice. I don't know if that's actually her taste, or if that's a calculated decision, that she's putting this look forward into the world, because she knows it can mask and hide who she really is and the terrible things that she's willing to do to get and maintain the tiny, insignificant amount of power that she has. It’s a power trip.
I think some bullies (not all) generally have low self esteem. And so any little bit of power they can get, they make it bigger so that it gives them worth. Maybe the toad is doing the pink to throw people off to hide what she really is. Or maybe she does actually see herself as this benevolent, nice woman. Because there's evidence of that, when she says to Harry "You know, deep down, you deserve to be punished". It does really raise the question of whether or not, if she's putting on a front deceitfully, or if she really, truly believes that that's what she is? And that the ends of this nice, sweet, ordered, perfect, Ministry-approved life, all the means to get to that end are justified?