I would like to say first off that I do not speak for the entire pagan or wiccan community, these are the views and applications of a 26-year-old Celtic/Eclectic witch and pagan, otherwise known as me, ierne.

The colour spectrum has a wide range of effects on the human psyche. In some wiccan/pagan paths, colour therapy is combined into the crafting of spells; for health, peace and well-being, love, and personal growth.
We have all heard of the White Light, which can be associated to by almost all cultures on Mother Earth. It's view is taken differently for different religious paths; most pagans tend to see and feel the Light as harmonious, the manifestation of warmth, love, friendship and spiritual wholeness.

I tend to see colours a bit more brightly than I used to, greener greens, bluer blues. This I believe develops when you become more spiritually aware of your surroundings. Look closely at a living tree or plant...soften your gaze...can you see the ivory light encircling the plant? That is the spirit energy...the Aura. I have been studying for fourteen years, and have only in the last couple of months learned to see the Auras of various plants and animals, (and a few humans too!!). This is a step, which takes time and practice, so don't feel bad if you can not see yet.

Well, enough rambling...on to the true content of my writing. In specific situations, the use of colourised breathing techniques are utilised to bring feelings of calmness, warmth, centring, healing, and intuitiveness. These techniques are usually combined with meditation and visualisation.
A technique for this follows, preceded by a list of colours and their appropriate uses...as found in my personal journal.

The colours I list here are also used for candle spells, and ritual clothing. It's an all-purpose list!

White-
As stated above, and can be used to substitute any of the other colours.

Black-
Often mis-represented as evil, black is simply an absence of all other colour. I personally use black in visualisation to represent the negative energies. This is a personal choice.

Blue-
This colour is used for healing and relaxation, and also for psychic awareness.

Purple-
Used to deepen personal spiritual awareness, as well as working with the divine power.

Red-
This is used for visualising love, protection, and also for connection to the God in his youthful aspect.

Orange-
This is wonderful for raising your energies.

Yellow-
Excellent colour for divination, as well as charm, confidence and attraction.

Green-
The herbalist's colour. Also, fertility, good luck, prosperity, and rejuvenation.

Brown-
Improve powers of telepathy, concentration, and also for the protection gained from familiars and pets.

Grey-
Useful in neutralising negative influences.

Gold-
Used to honour solar deities and attract their power.

Silver-
Used to attract the Goddess' influence. Also used to banish negativity, and bring about stability.

Find a place where you will be seated comfortably, (preferably cross-legged or Lotus position) maintaining correct posture while relaxing all muscles.
I do ask that if you tend to fall asleep or float on the astral plane, please lie down. I wouldn't want anyone bumping their head if they fall over!
Now, place your hands on your knees, (or beside you), palms facing upwards, as this will help you remain open. Drawing slow, deep breaths; in through your nose, and out through your mouth; visualise your need, the corresponding colour, and your personal power.
Visualise yourself breathing in the appropriate colour, and exhaling either black or gray, symbolising the negative influence or energy. I usually suggest this exercise have a time length of ten minutes, with five minutes of grounding or centring afterwards.
Burning a candle of the corresponding colour also seems to help, as well as your favourite incense.

I hope this has described the sometime pagan use of Colour Therapy well, and that it may help others also.