ANSI terminal colors are somehow dimmed
OK, I don't know if this is a bug or what, but I found a very effective solution/workaround.

In Preferences > Profiles > Text > ANSI Colors:

Set the Blue (4) color to 0% opacity and then in

Background > Color &amp; Effects:

if I set the opacity to 99% instead of 100%, the previously illegible text looks GREAT. Totally clear and legible, exactly what I wanted. But weirdly, setting 100% opacity makes it completely low-contrast and illegible. Leaving Blue (4) at default is still legible, but lower-contrast.

So again, not sure if the 99/100% opacity thing is a bug, but this works.