Curve nodes have no line showing Whenever I add a node that constructs a curve, e.g. RGB in cycles, or interpolation in Animation nodes. I can see and add points, but there is no line or curve connecting them, and I cannot find any options to change this.

I've probably broken something, but I can't find what!

Here's an example.
I have seen this issue before, I believe it is a bug in the UI theme, since it only seems to happen with certain bundled themes

After fumbling around with the settings I could not find any way to fix it, or what color to change, so this is more of a workaround than an actual fix.

For the time being just change the current theme in the user preferences, either permanently or temporarily while working with nodes.