Any 2.80 build.
I'm not sure that this is the perfect place to report this since it's not exactly a "bug". If this is not the right place, please feel free to point me in the right direction.
See attached image to see a muted and a non-muted Value node under the current Dark theme.
Now my eyes are not perfect(they are in fact quite bad) but I'm not colorblind and I find it extremely difficult to tell the difference between those two reds. Difficult enough that this just caused me to go troubleshooting my nodes for 15 minutes only to find out one of my values was simply muted.
To avoid this from happening, the behaviour for muting should either be changed(for example turn the entire node a different color rather than only the header, or add a red cross across the entire node) or themes as a rule of thumb should avoid using red color under the Node Editor category (Except for Output nodes, since those cannot be muted afaik), and the current default themes should be changed to follow that rule of thumb: