Arc Yellow and several of the other Paul-son colors have fluorescent dye added. The visible light seen by the scanner seems to be overpowered by the strong fluorescence and the colors come out "wrong". Hot Pink does this as well.

I found my new Epson Photoscanner "Perfection 1670" does a much better job than my older HP Scanners. See the post I did on Paulson samples a few minutes ago for an example. My guess is they use different kind of photosensor, but I haven't researched it.