How to make Natural colours

Green
Dry Colour:
Use mehendi / henna powder, separately or mix with equal quantity of any suitable flour to attain a lovely green shade.

Make use only pure mehendi and not the one mixed with amla (meant to be applied to our hair) as this would be brown in colour. Dry mehendi will not leave colour on your face as it can be easily brushed off. Only when it is a paste (i.e. it is mixed in water) will it leave a slight colour on your face. Thus, it can be used as a pucca / fast colour.

Many people like smearing other person's hair with colours. How about doing it with mehendi powder and saving a trip to the parlour?

Other methods
Dry and finely powder the leaves of Gulmohur (Delonix regia) tree for a green colour.
Crush the tender leaves of the Wheat plant to obtain a natural safe green Holi colour.

Wet colour:

Mix two teaspoons of mehendi in one litre of water. Stir well.
Green colour can also be obtained by mixing a fine paste of leaves like spinach / palak, coriander / dhaniya, mint / pudina, tomato leaves, etc. in water.

Yellow
Dry colour:
Mix two teaspoons of haldi / Turmeric powder with double quantity of besan (gram flour). Haldi and besan are extremely healthy for our skin, and are also used widely as a ubtan while taking bath.

You can use the ordinary haldi or "kasturi" haldi which is very fragrant and has enhanced therapeutic effects. Besan can be substituted by atta, maida, rice flour, arra rot (ground nut) powder, fuller's earth (multani mitti) and even talcum powder.

Another Method

Flowers like Amaltas (Cassia fistula), Marigold / Gainda (Tagetus erecta), Yellow Chrysanthemums, Black Babul (Acacia arabica) yield different shades of yellow. Dry the petals of these flowers in shade and crush them to obtain a fine powder. Mix appropriate quantity of the powder with besan, etc. or use separately.

Dry the rind of the Bael fruit (Aegle marmelos) and grind to obtain a yellow powder.

Wet Colour:

Add one teaspoon of haldi to two litres of water and stir well. This can be boiled to increase the concentration of colour and further diluted.
Soak Amaltas (Cassia fistula) or Marigold / Gainda (Tagetus erecta) flowers in water. Boil and leave overnight.

Red
Dry Colour:

Red Sandal Wood Powder / Raktachandan / Lalchandan (Pterocarpus santalinus) has a beautiful red colour, is extremely beneficial for the skin and is used in face packs, etc. This can be used instead of Red Gulal.
Dry red hibiscus flowers in shade and powder to make a lovely red colour. To increase the bulk add any flour to it
Sinduria, called Annato in English has a water chestnut shaped fruit which contains lovely brick colour red seeds. These yield both dry and wet colours.

Wet colour

Put 2 teaspoons of Red Sandal wood powder in a litre of water and boil. Dilute and use.
Peels of Red Pomegranate boiled in water give red.
For a bright orangish-red, mix thoroughly a pinch of chuna / lime powder (the one that we eat with our paan / betel leaves) with 2 spoons of haldi/ turmeric powder and a few drops of water. Use only after diluting with 10 litres of water.

Extracting red from flower petals

Buras (Rhododendron arboreum) known as Burans in the Garhwal hills and Brans in the Kumaon hills gives a lovely red colour when soaked in water overnight.
Red hibiscus flowers soaked in water overnight give a red which also has medicinal value.
The Palita Madar / Pangri / Indian Coral tree/ (Erythrina indica), found commonly in coastal regions, has large red flowers. Soak the flowers in water overnight.
Boil wood of Madder Tree in water for a deep red.
Red colour can also be obtained from juice of tomatoes and carrots. This can be diluted with sufficient quantity of water to remove the stickiness.

Blue
Dry Colour

The Jacaranda flowers can be dried in the shade and ground to obtain a beautiful blue powder. The flowers bloom in summers.
The blue Hibiscus which is found in Kerala can be dried and powdered just like the red hibiscus

Wet Colour

Crush the berries (fruits) of the Indigo plant and add to water for desired colour strength. In some Indigo species the leaves when boiled in water yield a rich blue.

Magenta
Wet Colour

Slice or grate one Beet root. Soak in 1 litre of water for a wonderful magenta. Boil or leave overnight for a deeper shade. Dilute.
Boil the peels of 10 - 15 pink Onions in half litre of water for an orangish-pink colour. Remove the peels before using to remove the smell.
Soak Kachnar (Bauhinia variegata) flowers (pink variety) in water overnight, or boil for a pinkish colour.

Saffron
Wet Colour

The Flame of the Forest (Butea monosperma), known as Tesu, Palash or Dhak in vernacular languages, is the source of the wonderful, traditional colour for Holi. The flowers are soaked overnight in water and can also be boiled to obtain a fragrant yellowish - orange colored water.
The dried flowers can be dried and powdered for a orange powder. Legend says that Lord Krishna used to play Holi with Tesu flowers, and the flowers also have a lot of medicinal properties. Tesu blooms during month of March.
Boil flower petals of red variety of Semul / Silk Cotton (Bombax ceiba ) in water.
Collect and dry the stalks of Harashringar / Parijatak (Nyctanthes arbor-tristis) flowers during the early winter season. Soak them in water to get a pleasant coloured orange.
Mix a pinch of Sandalwood powder from Ujjain (also used in our temples) in one litre of water for an instant, beautiful and fragrant saffron colour.
Soak a few stalks of Saffron / Kesar in 2 table spoons of water. Leave for few hours and grind to make a fine paste. Dilute with water for desired colour strength. Though expensive, it is excellent for our skin.

Brown
Wet Colour

Kattha (Acacia catechu), the one eaten in pan, when mixed with water will give a brownish colour.
Boil Tea or Coffee leaves in water. Cool and use.

Black
Wet Colour

Boil dried fruits of Amla / Indian Gooseberry in an iron vessel and leave overnight. Dilute with water and use.
Extract juice of black grapes and dilute with sufficient quantity of water to remove stickiness