It is important to note that a list of approved colourants allowed by regulatory bodies can vary from country to country. In addition, it is important when developing the formulation to think about factors that affect the shade and stability of the colour agent in order to achieve a final product with the same colour during the whole shelf life.
Dyes - Water soluble colouring agents
Pigments - Water insoluble colouring agents, they can be dispersed. Example: Iron Oxide
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Colourants can be classified as water-soluble "dyes" and water -insoluble "pigments" or "lakes".
Soluble colourants offer tinctorial strength exhibited when dissolved.
Water insoluble colourants may offer better opacity and stability, no problems with colour migration.