This technique has become fashionable in the last year or so and highly promoted by Guy Tang the top hairdresser from Los Angeles. There are many ways you can have technique applied to your hair either in a subtle way or with the boldest colours you can imagine. Pastels are also suitable on pre lightened hair.
This involves using three or more shades with the darkest at the top on the scalp and the lightest shade on the tips. You smudge the colours together with a paint brush so they blend seamlessly into each other. Please see the video!