[ This is based on partial information. Please help verify and/or expand these findings. ]
When Emacs runs in a non-windowed session its color reproduction capacity is framed or determined by the underlying terminal emulator (More accurate colors in terminal emulators). Emacs cannot produce a color that lies outside the range of what the terminal’s color palette renders possible.
This is immediately noticeable when the terminal’s first 16 codes do not
include a pure black value for the ‘termcol0’ entry and a pure white for
‘termcol15’. Emacs cannot set the correct background (white for
modus-operandi; black for modus-vivendi) or foreground (inverse of
the background). It thus falls back to the closest approximation, which
seldom is appropriate for the purposes of the Modus themes.
In such a case, the user is expected to update their terminal’s color palette such as by adapting these resources:
! Theme: modus-operandi ! Description: XTerm port of modus-operandi (Modus themes for GNU Emacs) ! Author: Protesilaos Stavrou, <https://protesilaos.com> xterm*background: #ffffff xterm*foreground: #000000 xterm*color0: #000000 xterm*color1: #a60000 xterm*color2: #005e00 xterm*color3: #813e00 xterm*color4: #0031a9 xterm*color5: #721045 xterm*color6: #00538b xterm*color7: #bfbfbf xterm*color8: #595959 xterm*color9: #972500 xterm*color10: #315b00 xterm*color11: #70480f xterm*color12: #2544bb xterm*color13: #5317ac xterm*color14: #005a5f xterm*color15: #ffffff ! Theme: modus-vivendi ! Description: XTerm port of modus-vivendi (Modus themes for GNU Emacs) ! Author: Protesilaos Stavrou, <https://protesilaos.com> xterm*background: #000000 xterm*foreground: #ffffff xterm*color0: #000000 xterm*color1: #ff8059 xterm*color2: #44bc44 xterm*color3: #d0bc00 xterm*color4: #2fafff xterm*color5: #feacd0 xterm*color6: #00d3d0 xterm*color7: #bfbfbf xterm*color8: #595959 xterm*color9: #ef8b50 xterm*color10: #70b900 xterm*color11: #c0c530 xterm*color12: #79a8ff xterm*color13: #b6a0ff xterm*color14: #6ae4b9 xterm*color15: #ffffff