[OzStarGazer]

Thanks, Brent. I meant the halo around Saturn. I could also see the rings (separately and much sharper than the halo). The halo was huge all around Saturn and its rings. The contrast was even bigger with the UHC filter. The red rim only appears with the UHC filter. It is very thin and like an outline (not a complete outline though - it resembles an arc in spherical objects for example, not the complete circumference). Sometimes I also see some green with the UHC filter. I have found other people who mention this problem with UHC filters on the net (if it is a problem).
PS: I think the term "planetary nebula" had confused me a bit because I thought one could call the halo around certain planets "nebula".