The spectral transmission graphs discussed on May 2nd require some mental effort which is not really necessary for understanding the issues with UV filters. Let your own eyes be the judge instead, and see the Spectral Transmission page for more thoughts on the Hoya and B+W filters shown below. the Hoya is not neutral should be readily apparent. That does not make it a “bad” filter, but it is a factor to be aware of if you are seeking to maintain the natural color balance of your lenses, especially the exquisitely color-matched Zeiss ZF line.
Hoya Ultra UV(0) at left, B+W 010 MRC at right