90% is a gross exaggeration. The Mail app is pure black[0]. Apps that have grey on black like Messages have styles carried over from the light version of apps — they weren’t specifically optimized for dark mode to improve readability. Other apps that I’ve checked: Music, Phone, Photos, Files, Calendar, even Twitter.
Blues exist along a range of brightness values and blues work great in dark terminals and editors all day every day for many many people. I'm typing into a browser window surrounded by probably about 4 or 5 terminal and editor windows peeking out of the background with somewhere between 5 and 10 different shades of blue on dark grey backgrounds and they look clear, bright, and amazing. The dark background makes the blues pop.
or green like the Hombebrew default scheme in Terminal. non-techy people I used to work with called me the matrix because my screen was stacked with multiple terminal windows with the green text on dark background color scheme
