She used Pure Tinctoria's cutch (Thar) to dye the paper pulp with a varigated effect. Here's how she did it:
For a varigated effect to the paper, just dissolved the dye in water as you would do normally and stirred it into the pulp.
For a more even colour, mix the dye colour in the water for the paper vat, before you add the pulp.
I think it's really beautiful!