Working in 10.4: dropper only works on main display, not extended

[Ninetrees]

Features working: change font, applying theme. Glad this is here, though my main editor is EditPad Pro.
At first, could not figure out why the dropper didn't work. 1. The button color is reversed to me, so I thought it was enabled when it was disabled...AND the dropper only works on my first display, not the extended, so when I thought it was enabled it didn't work.
I don't know what 'Use defaults for' Foreground and Background are supposed to do.