Editors don't update colors when changing dark mode

When in dark mode on a Mac (and presumably other systems), when you change to light mode, some of the background colours change, but not all. This is because we override some of the colors, in editors, but treat them as constants for the lifetime of the app, while others just use the standard palette.

For example, this is what you get when changing from dark -> light on OS X.

The fix for this is likely quite invasive as it involves replacing use of constants with dynamic lookup that is dark-mode aware.