Hi Markus,
Merry Christmas! As I recall this ink installation is in an old 7900 printer that you were trying to recover one or more clogged heads in. I assume that you recovered the print head and are now installing the Piezography Pro inks after PiezoFlushing the printer. The red in the inks is PiezoFlush. Normally, a single INIT FILL moves ink from the inside of the cartridge to just past the print head. There will be some residual mixing of the PiezoFlush with the ink as the ink enters into the ink dampers of the ink exchanger. And this is normal to some extent - requiring some amount of printing until the residual stain is gone. OR - run a second INIT FILL to really clear it!
best regards,
Jon