I never noticed that readings and meanings have black and white background 
The idea to put it into different regions of the screen is good, reading something is not a visual clue. But looking at black/white now is probably enough for me and a bit better than switching from reading Japanese to English for every item.
I think you were muddying your own waters by giving the reason that you want to input “hitori”, it is at least debatable. Apart from what a “meaning” is, beginners could start to input Japanese only and ignore to learn the English meaning because they are never punished for it. You also say that you want to enter the romanji version sometimes, but not always.
Look at it this way: WK asks you to reproduce what you were taught, which is a text string labeled “reading” and “meaning”. You didn’t learn “hitori”=“meaning”, so it is wrong from WK’s point of view. You add it to the synonyms and it becomes valid. (Also, in WK not all meanings of kanji are included. Is it “wrong” to enter a dictionary meaning not listed by WK?)
. Wow…I feel…not observant. 
) becomes a (minor) source of anxiety rather than a friendly “oops”. “Bouncing” that kind of mis-directed answer would be much less discouraging than buzzing it wrong.
Maybe part of why this is frustrating is that I’m an intermediate learner trying to get to the place in WK where I’m actually seeing some challenging content, and it’s (as everyone knows) slow to slog through the SRS process while getting to my prior learning-level. So I’m tempted to go along typing and submitting pretty fast, because it’s … necessarily pretty mindless (or pseudo-hypnotic, as 