Hi all,
thanks for your replies. I've just tried this again. Still no luck.
I can't see any change in colour when I mouse over the hoops (I've tried moving across and around them, hovering over them - nothing helps),
It occurs with the hoop for each axis,
I'm on Cura 4.3.0 so it shouldn't, I guess, be the same issue as reported by @NickB
I should also say that when I started with Cura a few weeks ago it was Cura 4.2.1 on Ubuntu 18.04 - I had the same problem then. I have since switched up to Cura 4.3.0 by grabbing a newer .AppImage (same problem) and then upgraded to Ubuntu 19.10.
Cheers,
Dean