Vocabulary Stickers are designed to make use of the amazing power of spaced repetition learning and color coding principles.
Spaced repetition means exposing yourself to the same piece of information at regular intervals to move it into your long term memory. As you can see in the graphic on the left, exposing yourself to a given information over several days helps you attain that piece of information in the long-term memory. Spaced repetition is a scientifically proven method to memorize information and increase vocabulary size in foreign languages.
Colour coding is a principle for remembering difficult to distinguish elements by use of different colours. In language learning this is for example used for subconsciously learning correct articles for a noun or the right tones in Chinese (e.g. der in blue, die in red, and das in orange for German).