dark green? The color used is light green.

It's "green", i.e., #ffff00.

/* Function markers are enabled from View->View Properties->Cell Markers */
GnmItemGrid function-marker {
  color: green;
  border-color: #555555;
  /* See also GnmPane */
}

I never use this myself, so I don't care much.  Any suggestion as to what
colour fits better?  Use ~/.config/gtk-3.0/gtk.css for testing.

Anyone against this?

GnmItemGrid function-marker {
  color: #80ff80;
}

Actually I think it would be nicer to choose one of the colors from GNOME's palette:

https://developer.gnome.org/hig-book/3.10/design-color.html.en

I think any of the Hilight colors (green, red, purple, blue) would work fine.  I might lean slightly toward blue (#9DB8D2) since it looks similar to the color of the arrow toolbar button which enters a calculation, in the default Adwaita theme at least.  But, again, any of these could work.

None of the green choices seem to work any better than plain green.
Most are about as dark as plain green.  Hilight Green isn't really green:
it's gray.

I am not sure how much LSD went into that process.

So #80ff80 it is.


This problem has been fixed in our software repository. The fix will go into the next software release. Thank you for your bug report.

I don't think it is necessarily the fill colour that is interfering but the border. I think

/* Function markers are enabled from View->View Properties->Cell Markers */
GnmItemGrid function-marker {
  color: #80ff80;;
  border-color: #80ff80;
  /* See also GnmPane */
}

would in fact work better.

I agree that the border is much of the problem.  I think a faint gray border would be better than none, e.g.

GnmItemGrid function-marker {
  color: #80ff80;
  border-color: #70a070;
}