Terminal background is off (too dark/too light) with retrobox in MacVim

[lifepillar]

Using retrobox with MacVim r177 (Vim 9.0.1677), it appears that the background (and the foreground, too, perhaps?) are off, as in the screenshots below (the issue is more prominent with light background). Does anyone reproduce this issue? In terminals (I have tried iTerm2 with termiguicolors and Terminal.app without termguicolors) the colors are correct. On the other hand, other color schemes in MacVim do not have any issue (I have tried a few: darkblue, desert, peachpuff, sorbet, etc…: all fine), so I am a bit at loss why this is happening just with retrobox. It is not happening with Gruvbox 8 either.