This was done using black paper and paper that had been sprayed with different colour inks and allowed to blur and mix together on the paper.
It is supposed to resemble a stained glass window. I think the inky paper helps create the same effect.
Sketch of print block layout & 2 prints on paper.
Zoom of Yellow print above.
Black ink printed onto tracing paper. I also added coloured tissue paper underneath, to define different areas.