What it is is felting done with coloured wool and then a bit of Chris crossing wraps with coloured embroidery thread. To add colour of this brightness you would have to first bleach out the natural colour of your dreads and then add vibrant colours, but as you wash your hair the colours would fade quite quickly.
I did these pics for inspiration as i'm felting a good few of my dreads, i am adding with a felting needle, but don't worry SE it is only felted on the ends of my own dreads - its easier to make up the coloured dread first then add to your own dreads
wow so fun & colorful! looks great