There used to be a bugette, which might still exist, in Guide such that labels can end up being drawn the same colour as the last TDF object to be printed before those labels are printed. Dunno if it's still there, but basically say you plotted something infrared with a red symbol, and turned the labels on, the labels would be plotted in the same shade of red.

And the next set of labels plotted after that could sometimes also end up printed red, if the object was a star and not another symbol with its own colour.

Whether that is still the case or not, I know not.

But what can happen in special sets of circumstances, through sheer happenstance, is that labels can be there, but end up being plotted in black, which, on a black background, kind of doesn't show much.

One way to test this half baked idea is to have isophotes activated, so the Mikly Way is plotted or something. Say go to Cygnus, select level 3, and if the labels are in black, they'll show up against the grey Milky Way.

Incidentally, I've just noticed common star labels are not plotted at level 2, so somewhere in Guide is a setting for field width when such labels are to be plotted, that could've also suffered bad setting.

You could also try using the Background option to plot in a red scale, for night vision mode, where everything is plotted in 'redscale' (like greyscale, but red), as if the labels are being plotted, but plotted in black, for whatever reason, they may show up in that mode.

If they aren't being plotted, they aren't being plotted, fair enough. I suppose you've checked that they aren't being plotted at all zoom levels?

Cheers

John