Added/removed file contents displayed with poor color combination

I'm using meld on GNU/Linux Mint 18.3 with XFCE4; and it's either the packaged v3.10 and just-downloaded v3.18.

Now, when I meld two folders, and one has a file missing from the other (i.e. added/removed file) - opening that file shows me the contents in very-dark-gray font over pitch-black background - obviously quite unreadable. Colors are otherwise reasonable - white background, black text, and pastel-ish highlights for additions, removals and changes of lines.

The Preferences menu doesn't seem to have an option to change the color combinations.

Now, I'm not sure whether it's an issue with Meld itself or the distribution, but there should be an obvious way to rectify this - and there isn't.