"bright yellow on white" and "dark blue on black": I thought the system was designed so that you should use a bright colors on a dark color or opposite, not two colors in the same group?
If that ever happens with a properly implemented terminal, it's an application bug. But buggy terminals are very common.
Sometimes it's due to COLORFGBG not being set.
Sometimes it's due to failing to implement the legacy "bold = intense" hack (from the 8-color days), which very many programs rely on.
Sometimes it's due to the colorscheme having all colors be too bright. It's abominable how far some of those colorschemes are from the VGA standard.
(Sometimes it's a gamma-ish problem. I can't believe it's $CURRENTYEAR and computer screens still vary so badly).
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Here's a quick test for several problems. These are bad color combinations that shouldn't be chosen, but they should be readable with just a bit of effort. Output is 2 lines, one offblack-on-black, one white-on-offwhite.
printf '\e[3%d;1;4%dmThis should be (barely) readable.\e[m\n' 0 0 7 7
Results with default configuration on Debian stable:
alacritty: fail (no obvious configuration)
cool-retro-term: pass (despite deliberately neutering color)
deepin-terminal: marginal pass (colorscheme too bright)
Eterm: pass
foot: fail (no obvious configuration; buggily packaged as X11 despite being Wayland-only)
gnome-console (really?) = kgx: fail (configuration does not contain an obvious fix)
gnome-terminal: fail (need to go into preferences and check "show bold text in bright colors")
kitty: fail (no obvious configuration)
konsole: half-fail (colorscheme too bright)
linux: pass
lxterminal: fail (check "bold is bright" in preferences)
mate-terminal: pass
mlterm: pass
pangoterm: pass
pterm: pass
qterminal: pass
rxvt: pass (it, along with its derivatives (I don't remember which right now, but several are probably listed here), has other unfixable bugs though, and should be avoided unless you are deliberately trying to write a program that works even with abominable terminals)
sakura: fail (no obvious configuration)
stterm: marginal pass (colorscheme too bright)
terminator (the gnome one): fail
terminology: pass
termit: fail (configuration does not contain an obvious fix)
tilix: pass
xfce4-terminal: pass
xiterm+thai: marginal fail (colorscheme contrast too low in both directions somehow)
xterm: pass
yakuake: half-fail (as konsole)
zutty: marginal pass (colorscheme too bright)
(not that this test is only for colors, not for the many other features you might expect a terminal to support)
