Regulatory agencies like the US Food and Drug Administration [FDA] and the European Food Safety Authority [EFSA] manage and regulate the usage of synthetic colours. They allow only a few types of synthetic colours to be used in food. They are:

1. Yellow No. 6/Sunset Yellow: This colourant of orange-yellow colour which has applications in candy, sauces, baked goods and preserved fruits.
2. Yellow No. 5/Tartrazine: This colourant of lemon-yellow colour which has applications in candy, soft drinks, chips, popcorn and cereals.
3. Red No. 40/Allura Red: This colourant of dark red colour which has applications in sports drinks, candy, condiments and cereals.
4. Red No. 3/Erythrosine: This colourant of cherry-red colour which has applications in candy, popsicles and cake-decorating gels.
5. Blue No. 2/Indigo Carmine: This colourant of royal blue colour which has applications in candy, ice cream, cereal and snacks.
6. Blue No. 1/Brilliant Blue: This colourant of greenish-blue colour which has applications in ice cream, canned peas, packaged soups, popsicles and icings.

The USFDA and EFSA have a few exceptions. E.g., in the US, the FDA allows Green No. 3 or Fast Green FCF unlike the ESFA and in Europe, the EFSA allows Quinoline Yellow, Carmoisine and Ponceau unlike the FDA.

In India, the regulatory agency is called the National Food and Drug Administration and Control (NFDAC). The following food colours are permitted in India: Yellow No. 6/Sunset Yellow FCF, Yellow No. 5/Tartrazine, Red No. 3/Erythrosine, Red No. 18/Ponceau 4R, Red No. 10/Carmoisine, Green No. 3/Fast Green FCF, Blue No. 2/Indigo Carmine, Blue No. 1/Brilliant Blue FCF.

In all, there are 3 main categories of food colours. They are Primary Food colours, Blended colours and Lake Colours. In detail they are:

Organic pigments come in the following types:

1. Carbon pigments: Examples include Carbon Black which comes from natural gas, Acetylene Black from Calcium Carbide, and Lamp Black which is derived from the soot of imperfect combustion of natural oils.
2. Lake pigments: Lake colour or lake pigments are pigments derived from precipitating soluble dyes in metallic salts. Some examples of lake colours include indigo lakes, carmine lakes and rose madder lakes.
3. Non-ionic organic pigments: These pigments are usually of azoic type. They include diazo pigments, monoazo pigments which produce colours in the reddish-yellow spectrum, polycyclic pigments, phthalocyanine pigments such as phthalocyanine blues and greens, perylene pigments, perynone pigments, anthraquinone pigments, quinacridone pigments which produce red, violet and oranges, dioxazine pigments which produce violets, thioindigo pigments, isoindolinone pigments which produce yellow, orange and reds, pyranthrone pigments, and quinophthalone pigments.
4. Alizarin Pigment: This is produced through the root of the madder plant. It is also called Madder red and it imparts shades of red and red-purple.

Acid dyes have a variety of different uses. They are used in many different industries and sectors for various types of applications.

A few textile applications and uses according to the type of dye:

1. Fast Acid Dyes: Used for dyeing or colouring non-washable knitting yarns, carpet yarns and piece goods. It is possible that a few pale-medium shades of fast acid dyes may be able to be hand washed.
2. Super Milling Dyes: These can be used to impart bright shades onto products or materials like loose stock, sliver, and yarns that need high wet fastness. They can also be used to impart pale-medium shades that can be machine-washed.
3. Acid Levelling Dyes: Such dyes can be used to dye or impart colour onto materials like carpet yarn, woollen and worsted fabrics, and such textile products that do not need washing and perspiration fastness.
4. Acid Milling Dyes: This type of acid dye can be used to impart medium-heavy bright shades on products like piece goods and materials like carpet yarns, knitting yarns, and weaving yarns.
5. Metal Complex Dyes: Due to their fastness properties, these acid dyes are used to dye womenswear and hosiery and other materials like leather, wood, metals, plastics, etc.

Within the textile and fashion industry, acid dyes have many other uses. Furthermore, they also have uses and applications in other industries other than the fashion and textile industry. They all are:

1. Medical Industry: Acid dyes are used in the field of Histology for the purposes of research or diagnosis. They are used to stain or colour basic tissue proteins in microscopic examinations.
2. Food Industry: Acid dyes are used as food colouring in the food industry. They must be approved as being eligible for consumption before use. They are used in bread, condiments, frosting, etc.
3. Leather Colouration: Due to acid dyes being resistant to migration, they are ideal to colour leather. Usually, all types of acid milling dyes and metal complex dyes are applicable here.
4. Dyeing of Fur Skins: Due to a few of their properties like fastness, good exhaustion and combinability at 60 to 65 °C, and being able to impart only a light stain as well as trichromatic shades, acid dyes are good for fur skin dyeing.
5. Dyeing of Double Weave Cloths: One of the dyes used to impart colour only double cloths are metal complex non-bleeding dyes. Double weave cloths or just double cloths are a type of woven textile where different sets of materials like sheep skins, weft yarns, etc are interconnected to form 2 layered cloths.
6. Wood Staining and Coating: Wood is stained with colour to make it more attractive or to add colour to it. They can be stained in natural wood tones or another colour entirely. For this staining process, generally solvent soluble acid dyes are used. Acid dyes like metal complex dyes are also used to coat stained wood to increase durability and protection.
7. Ink Formulation: Acid dyes can also be used to make ink for different uses like ink-jet printers, ink pads, ink for ball pens, ink for markers, etc. coloured ink in trichromatic form can also be made.
8. Jute Dyeing: Jute fabrics and fibres are generally highly demanded to be bright, wash fast and light fast. For this reason, acid dyes with good light fastness properties are used to dye jute.

Colors hold a very important place in pharmaceuticals even though they have no use in the effectiveness of medicines. Their contribution is more psychological. Let us understand their importance:

1. 1. They provide tablets, pills, liquids, and other products with their own brands, identities, and the ability to be easily identifiable and recognizable by consumers.
   2. Adding a coating of color gives many products more stability and hence helps to increase their shelf life.
   3. Due to branding, advertising, and marketing, products are associated with their colors and hence can be immediately identified simply by their color (E.g., Digene has a unique light pink color). This helps consumers differentiate between real products and counterfeits.
   4. It is scientifically proven that people also eat with their eyes, thus, having an orange-flavoured pill that is also orange in color makes it more appealing for consumers to consume the product.
   5. Colors can also help differentiate between dosages. i.e., if the same pill comes in different intensities, having them be different colors will prevent overdosing.