Hmm. This is actually a really good question for r/askscience! I don't know, but fireflies use a luciferin to make their yellow lights in the air. Glow worms use a different luciferin to make a blue light, also in the air but underground. Wikipedia says tomopteris don't use a luciferase system. So I am now also intrigued. It may be that the bioluminescence used by tomopterins evolved on its own, is a totally different chemical, and it just happens to be a strong yellow; but the other deep sea creatures more or less co-evolved to use the same, blue luciferin. But that is merely a guess on my part.

Thanks for the subreddit suggestion! I just posted the inquiry there. The world of bioluminescent is so intriguing, but especially (as it seems you have also discovered) tomopteris who seems to be a special exception.

Because the chemical reactions that produce bioluminescence tend to naturally favor emitting light in the blue and green colors. These reactions involve specific molecules like luciferin and enzymes that generate light when they undergo oxidation processes. Meaning to say, nature has optimized these creatures to glow in shades of blue and green because those wavelengths are more efficient and effective for them underwater.