This is a meditation created by Walter Makichen who is the author of Spirit Babies - the pdf outlines his original guidance. 

If you prefer a guided meditation, his wife Mary-Frances Makichen offers an expanded interpretation of it here: Rainbow Chakra Meditation.

The intention is to cleanse each chakra. You'll focus on each chakra individually, visualizing its corresponding color and imagining its energy flowing up from the earth, through both of your legs, meeting at the chakra within your body, before crossing over and flowing freely back down the opposite leg into the earth.