Now that I’m halfway through WaniKani, I’m really seeing the need to know which reading is which, and I feel like while WaniKani tells you which one you’re learning when a Kanji is first presented to you, it’s largely ignored after that first encounter, and you only ever learn the other reading with vocabulary. I’d appreciate it if there was some indication on the Kanji review page of which reading WaniKani was looking for. Changing the background color is probably too much, but something like hint or synonym text below the kanji that says (OnYomi) or (KunYomi), right above where you type, would be great (though maybe in a different font, color, or size because we have to learn the readings for the on’yomi and kun’yomi vocab as well and don’t want to confuse that). This would also help all those people who learned the Kanji somewhere else and have no idea which one WaniKani wants. Sure, they can guess and not be penalized, but a simple indicator would make the shake unnecessary and would reinforce it for learners each time the practice.
Another additional indicator would be to show what you type in Katakana instead of HIragana for OnYomi. This seems to be a fairly common additional way to distinguish which readings are which in online dictionaries when giving information about a kanji. I think these two tweaks would greatly help people learn which reading is which as you practice the kanji over and over, which in turn helps pick the right reading for the subsequent vocabulary that uses those characters.