N.Y.P.D. Blue and the color purple

I know its the last season, but they are using some sort of "sixth sense" ploy with purple instead of red.
The logo is now purple, most of the cast (including guest stars and some extra's) wear purple shirts, with some notable exceptions. The co-star Mark Gossler..i think ? (Sip's partner) never does. "Medavoy" (Gordon Clapp)doesnt either, along with the new blond female detective and a few more. I'm a big fan of subtext in media, so it has got my interest at the moment.