Simply tell yourself that you will devote the next period of time to colour healing. Take as long or as little time as you can and want.
Get to know the colours. The colours used for colour healing are freely available in the nature around you. Take a walk in a park, botanical gardens, open fields, woodlands, marshland, the desert, mountains, the beach, wherever! At some point in this walk, stop, stand still and mentally select a plant or flower. Observe it closely in its natural habitat, trying to identify the hue, saturation and lightness of its colour.
Now close your eyes and try to reproduce that colour in your mind's eye. Try to recreate the colour as intensely and as accurately as possible. After a few moments, open your eyes and 'check' this inner colour against the actual outer colour. Are they a close match? If not, don't worry simply try again. If they do match, continue your walk until you find another plant/flower that attracts your attention. Repeat this exercise as often as you can. Don't forget to breath deeply and evenly.
Practice makes perfect. The more often you can manage to do the above exercise, the more skilful you will become.
When you have learnt to remember the colour of your choice try to send it - project it - into certain parts of your body.
How? You can imagine the colour/energy leaving your hands and flowing from your fingertips, or you could send it from your third eye, the space between your eyebrows, or from your heart chakra. Or you could find your own technique. You could also send it to somebody else. This activity is called Abesnt Healing.
When you become more skilful in doing colour healing for yourself and/or others you will develop intuition. This is a feeling, perhaps an inner voice, which guides you toward the most appropriate colour and where to send it.