The colours of your primary chakras are arranged like a rainbow, with red at the root and violet-white at the crown. There are some schools of mysticism that arrange the colours differently, but simplicity is best, so for the purposes of this meditation, stick with the rainbow colours.
The basic plan of this meditation, is to focus on each chakra in turn, from the root up, and bathe yourself in coloured light using your imagination. If you have difficulty imagining the colours, then grab a CD rom disk from your computer, and be inspired by the laser perfect rainbows you can see on the back. Focus on the colour you need, and draw it into yourself, from that.
Start this meditation, by getting grounded. When you are grounded, focus on the area of your root chakra, and imagine the red fire that is there. Imagine the red colour expanding to fill your whole aura, and then expanding further to fill the whole room. (Best if there is no-one else in the room with you, unless they are also doing the meditation.) Then pull it in and compress it, shrinking the red light to a tiny pinpoint, as small as you can imagine. Then pop it out room size again, and shrink it again. This is like a chakra workout!
Stretching and shrinking. When you have done that several times, let it expand from a pinpoint to its normal size.
Move onto the next chakra, the orange flame red-gold of the second chakra, and do the same thing. Continue with each chakra, moving up the rainbow.
The power chakra is golden light.
The heart chakra is green, the bright light green of a new leaf... you can do the heart chakra twice, the second time using the rose pink of unconditional love, but return to green afterwards.
The throat chakra is royal blue.
The third eye is purple-violet.
The crown chakra is pale violet-white.
When you are finished giving your chakras a workout, get grounded again, and use this affirmation: "I reset my four fields to their proper size and vibration."
You can do this meditation whenever you like.
A variation of it is to take a week to do it. Each day, wear clothes of the chakra colour you are focusing on, eat foods of that colour as best as you are able, and try to surround yourself in that colour as much as possible. Getting coloured light bulbs so you can bathe yourself in coloured light can be helpful. Meditate, focusing on the chakra whose colour you are wearing, and ask for help in clearing the chakra and tuning it to its fullest potential. You may get interesting insights about the purpose of each chakra, and what issues are there for you to clear.
If you like, you can add two more days to the meditation, the first day to focus on white and the last day to focus on black.
Black is not negative as some people think. It is simply the absence of colour, and it is associated with the Goddess. The space between the stars, the cosmic womb-void where creation takes place.(Kundalini Teacher)