I have tritanopia and have until this day in my life never known that I can't see yellow highlighter against white paper (just never was exposed to the issue). When I got given a highlighter today in the exam, I was freaking OUT because my paper was becoming soggy but I couldn't see the colour coming up.
I was like, wtf is going on, am I dreaming/hallucinating? I was like tapping the page and it was soggy with highlighter, but I couldn't see the colour at all. People could begin to smell it as well and saw that my whole page was practically scribbled in with yellow highlighter, and I couldn't explain to them what I had done until after the exam.
I spent a good 3 minutes in writing time trying to get the highlighter to work (which I had borrowed earlier in the morning).
Funny in hindsight, although I was seriously freaking out in the exam
WTF
How have you never used a yellow highlighter before!!!!!!!!!!
I don't know! I've used other colours all the time... just never yellow. I must have been looking at pages which have had stuff highlighted on them now that I think about it, and other people would have been showing me stuff with highlights, but I just would never have known and been reading over the whole thing and not just the stuff they've highlighted.
I figured it out when I googled it after the exam.
wow. Could you see the colour on the barrel/body of the highlighter?
EDIT: then again, yellow highlighter is ridiculously bright sometimes. I have normal vision and sometimes have trouble seeing yellow highlighter on paper if it's not particularly vivid/ink is running out.
It was a Stabilo Boss highlighter so the barrel is black, and this one happened to have a black lid as well (go figure, even that's abnormal for Stabilo Boss).
When it didn't work at first, I was just like wth is going on... staring at people around me thinking to myself "how do I ask someone in the last third of an English exam if my highlighter is working or not... isn't this one weird hell of a conundrum?"
For those that are curious...

yellow and white are almost identical to me