Red 40, a dye commonly used in processed foods, is a vegan-friendly ingredient. However, while it does not include any animal products, it is tested on animals.
The dye is made from coal tar and petroleum, so each batch of dye must be tested on rats and mice, who are then euthanized after the testing. While some vegans simply eliminate animal products from their diet, others take one step further and refuse to buy products that have been tested on animals. Ultimately, the opinion on whether Red 40 is vegan or not is up to the discretion of the individual vegan.