Might need changes to Adwaita to export that colour.

What colors are these? I can't find any reference to colors in gnome-mouse-test.c in git master.

Sorry, It's not yet commited, patches are there:

https://bugzilla.gnome.org/show_bug.cgi?id=579135

Cosimo?

I am not sure using symbolic colors from the theme here really buys us much. The graphic style of the test area is pretty specific, as it has to match the colors of the SVG asset drawn inside, and I don't think you want the elements around it to change too much with the theme.
We also cannot really use or add generic style classes, as the widget is pretty unique.

In any case, if you still think it's a good idea, I can provide a patch, but it's not particularly pretty: we essentially need to add those color defines to the theme with a control-center specific name, use gtk_style_context_lookup_color() and fall back to the same gdk_rgba_parse() calls when those fail.

(In reply to comment #5)
> I am not sure using symbolic colors from the theme here really buys us much.
> The graphic style of the test area is pretty specific, ...

I'm inclined to agree. Reopen if necessary.