Turns out the problem is caused by the theme I’m using (Divi by Elegant Themes), which is overwriting the color setting applied by Connections Gridder in it’s own style.css file (in the theme’s “span.fn” class definition.)
Workaround applied by modifying child theme css definition of span.fn
Thanks Steven, I appreciate the quick reply. I tried “color” but it doesn’t seem to work. Can’t get the text color to be anything but black. The background_color short code option works fine setting the background color, but not the text on top of it.