I just absolutely adore this symbolism in Death becomes her
I've never personally seen anyone talk about it so this is all my own interpretation.
So I'm guessing we all know the movie poster
What's always confused me about this is the way that Helen wears white and Madeline wears red, when for all the movie Mad has mainly been wearing white, and Hel later claimed red for herself.
Is what I thought, before rewarching it and realized that those colours come from Helens murder fantasy about Madeline. (I'm still not a hundred percent sure why they used the opposite colours for the poster, honestly..)
And that got me thinking. I'm certain that the change was a hundred percent intentional. This is Helen's fantasy, in which she imagines that she gets rid of Madeline, a.k.a regains her power over not just Mad, but also Ernest and her general life. Helen imagines that they can finally switch positions, Madeline plays the Helen, Helen plays the Madeline.
She's felt like Madeline was always the one in control, hurt her on purpose, and that she was forced to watch(possibly not even realizing how much she was hurting Madeline during that time as well or losing track of "who started it" ), and now if she gets this plan over with, Madeline will have to be the one not in control, and she will finally be able to rise to the top like her friend always has anf claim that power over everything for herself for once.
Her white dress also has correlation to the fact that Ernest wears a white suit though, I believe, as white dresses often relate to weddings, one which Helen never got. So in her fantasy, not only does she have the power, she also has the marriage with Ernest as the groom she never got to have symbolised(even if that part may just be for more conviction in terms of getting Ernest on her side) and portrays them as a couple, or simply a team.
She isn't the only one in this, for once she gets the man, and Madeline could be the one that faces the consequence or bad thing
In a way I figure that is is maybe just obvious and I didn't need to deepdive, but I genuinely love this little change from which you can draw do kuch so I just had to yap