Based on your comment, I’m sure you’ve learned how to navigate without using the colors as a guide reminder. With that being said, I’m going to take your comment as an opportunity to recommend a script that allows users to choose which colors appear on the dashboard, lesson screen, and review screen. It’s called WaniKani Custom Color Style.
Looking at the date of the last posting on that thread, I can’t guarantee if it is being actively maintained. There are other userstyle scripts on WaniKani, but I’m not sure if they go as far as to allow one to change the review and lesson screens.