The white light of a white/red PAPI system is too close to the colour yellow/orange
...depending on the installation and brightness setting. Some PAPIs are very distinctly white/red, some are closer to yellow/orange. Perhaps we should convince every airport to put proper lightbulbs into their PAPi projectors and change them regularly.
VIE used to have T-vasis on 16/34. Fun part was that its crossbar was made of four lights. "Your PAPI is not working, it shows four whites on the glide" calls on gnd frequency vere pretty regular.