Wikipedia

You mean the article that includes the quote explaining why it's not a thing:

, "Bi lighting often feels ubiquitous, even when there isn't a hint of bisexuality in sight [...] These are the colors of magic in fantasy, alien landscapes in sci-fi, and the neon lighting of cyberpunk settings and nightclubs. Thus, while Twitter users and media critics have noted bi lighting in John Wick 3, Blade Runner 2049, Color Out of Space, Orphan: First Kill, Bingo Hell, Men in Black: International, Bullet Train and Spider-Man: Into the Spider-Verse, there's often a less gay logic for doing so."

TLDR: the prevalence of examples where pink and blue light are used together without wanting to represent bisexuality make it useless as an indicator (at least on its own)

Not a thing.

I think their contention was that it was an established thing that this sort of lighting was bisexual.

According to BOWIE Creators, the concept of bisexual lighting was invented in 2014 by a Tumblr fan of Sherlock who believed that the lighting was being used to signal that Dr. Watson was bisexual and would eventually be in a romantic relationship with Sherlock Holmes.

Based on the history tab it seems more like an Urban Dictionary thing. The examples section has this:

Lara Thompson, a lecturer of film at Middlesex University, has argued that bisexual lighting is not well-known, stating: "I would have to see more examples before I see bisexual lighting as a wholly convincing phenomenon".

It seems to me like a form of symbolism that has happened a few times based on the wiki article rather than an established trope.

Well, technically it’s just a wave.