The colour markers printed on toothpaste represents the type of ingredient used in it
Multiple social media users believe that the colour coding on the edge of toothpaste tubes indicate towards the ingredients used in the toothpaste. [...] According to most social media users who post this popular myth, you should be paying close attention to the bottom edge of your toothpaste tubes. The small rectangle or square colour at the bottom, black, blue, red, or green, reveals the ingredients of the toothpaste: [...] No. The colour in the toothpaste tube doesn’t reveal anything about their ingredients. Colgate, one of the largest toothpaste manufacturers, mentions on their website, "Oral care companies don’t mark their toothpaste with coloured squares to try to trick consumers and hide ingredients from them."