Don’t you hate it when you type in the correct vocabulary answer, before noticing it was a radical or kanji review? I hate that too.
Here’s a tiny userscript (css really) to make the type of review item more obvious, by changing the position based on item type: radical (left), kanji (middle), or vocabulary (right).
For me, this makes it unmistakable which one I’m being asked for (because apparently changing the color, size, or label text aren’t enough for my feeble brain).
Reminds me of a favorite saying “You can make something fool proof, but you can’t make it damn-fool proof” 
Doesn’t stop me from trying though! Enjoy!
// ==UserScript==
// @name WaniKani Obvious Review Type
// @author jeff8v7
// @description Shows review item type in a more obviuos way: radicals on left, kanji in middle, vocabulary on right.
// @version 1.0.1
// @include https://www.wanikani.com/review/session*
// @run-at document-end
// @grant none
// ==/UserScript==
var css = '\
div#character.vocabulary { padding-left: 25vw; background-image: linear-gradient(to left, #a0f, #9300dd) !important } \
div#character.vocabulary + div { padding-left: 25vw; } \
div#character.vocabulary + div + div form fieldset input { padding-left: 25vw; } \
div#character.radical { padding-right: 25vw; background-image: linear-gradient(to right, #0af, #0093dd) !important; } \
div#character.radical + div { padding-right: 25vw; } \
div#character.radical + div + div form fieldset input { padding-right: 25vw; } \
';
$('body').append('<style type="text/css">'+css+'</style>');```