Boxes will show up under each kanji. Click the black portion of the box and a color picker will appear. Changes are automatically saved in your browser until cookies are cleared (may vary on what browser you use). Click Change Colors again to hide the boxes.
Download colors.json through Save Colors as JSON File and upload it from other devices through Load Colors from JSON File. Your colors will then be saved to the browser's local storage.
Click on individual kanji to hide/show meanings and romanji, or use the purple buttons to change visibility settings for all kanji.
More kanji, categorized by JLPT levels, option to filter based on category