The term DPP may refer to one of several pigments. DPP lacks a pigment code but may be Cosmoray Orange (Irgazin DPP)- the name Cosmoray can sometimes be conflated with PO73, so you might need to disentangle the two. According to Artiscreation, It may also refer to PO107 or PO108 (experimental). Both are reported to have excellent lightfastness. At the time of writing, it's offered by at least one major watercolormaker.
