Quoted from tiesmasc:
It should be solid only when a ball is already locked on castle playfield (or virtual locks are turned on)... AND you have qualified capture dorothy AND not locked a ball on the castle playfield yourself. Once you capture dorothy yourself then the light will not become unlit.
That's pretty much how I intended it to work, although the blue blinking was a copy/paste error.
We will have an update before too long that changes the "Capture Dorothy" lamp to work as follows:
off = unqualified
blinking yellow = qualified, no ball behind gate
blinking yellow/red = qualified, ball behind gate (this is to warn you that the ball will be released)
solid yellow = ball captured