For me, it's not just an "underline" issue. In my case, it's a "thin line" issue, and letters are usually made up of thin lines, especially the monospace font used here. But that's just me. (Side note: I still use monospace fonts in programming, I just choose one that has thicker lines in relation to the character size.)
For example, when I saw the website in question, I did not notice the red or green text color at all. I did see the underline, though. I didn't know it's significance, however, because the key is at the bottom of the examples (5 rows of blocks of text examples) rather than the top. Oddly enough, in this particular instance, the green of the text looks more like a light grey, and I can see the red better than the green. Normally it's the other way around, but it might have something to do with the particular shades involved.
Importantly, there are different forms of red/green colorblindness. For some people, the colors are literally indistinguishable. They look exactly the same.
Mine is a form of reduced sensitivity. I can see it if it's a large area. E.g., if you're wearing a red shirt, then I know it's red, and it looks completely different from a green shirt. If it's just a thin line of red, though, then I might not pick up on it unless I concentrate. It just doesn't stand out when the lines are thin.
Fabric can be weird for me. Some fabrics cause issue because they will use red threads interspersed throughout the cloth in order to achieve a red/pinkish overtone, and I won't notice it at all (unless I really concentrate on it). It's because the red is coming from thin lines. I have to be careful with tweed, for example.
I have the same kind (IIRC it’s called deuteranomaly).
I find increasing the brightness of the display helps, but it’s still a pain in the arse to distinguish the two when the lines are thin in this example.
If you have deuteranopia or deuteranomaly, you should be able to just about make it out. With normal colour vision, on the other hand, it’s meant to be nearly impossible to see.
Yeah, I definitely can't see it with my 'normal' colour vision. I did notice down in the comments there's a processed version that lets you see where the letters are, but even with that knowledge it's still impossible.
actually when I look at the processed version I can then make the outer ring of the O and about 70% of the last two letters. Like I can see oh there is that part of the letter - basically in the orange.
For example, when I saw the website in question, I did not notice the red or green text color at all. I did see the underline, though. I didn't know it's significance, however, because the key is at the bottom of the examples (5 rows of blocks of text examples) rather than the top. Oddly enough, in this particular instance, the green of the text looks more like a light grey, and I can see the red better than the green. Normally it's the other way around, but it might have something to do with the particular shades involved.
Importantly, there are different forms of red/green colorblindness. For some people, the colors are literally indistinguishable. They look exactly the same.
Mine is a form of reduced sensitivity. I can see it if it's a large area. E.g., if you're wearing a red shirt, then I know it's red, and it looks completely different from a green shirt. If it's just a thin line of red, though, then I might not pick up on it unless I concentrate. It just doesn't stand out when the lines are thin.
Fabric can be weird for me. Some fabrics cause issue because they will use red threads interspersed throughout the cloth in order to achieve a red/pinkish overtone, and I won't notice it at all (unless I really concentrate on it). It's because the red is coming from thin lines. I have to be careful with tweed, for example.
But again, that's just my experience.