Kinda unrelated story:
I ran into trouble using "true black" (A combo of CMYK) on a van wrap. In all the testing I did, it looked fine, but outdoors, it looked green. But photos of the wrap looked fine. (the camera has a uv filter?) Figured out that the cyan ink fluorescenced in daylight with that combo of ink and material at least. And converted it to just black ink for the next ones.
Is this why you see a lot of web pages that are some mid-shade grey background with another mid-shade grey text, resulting in extremely low contrast and increased difficulty in reading?