By the very nature of UV light, fitting a UV filter to cut it out can lead to very slight warm results....so many variables, e.g what altitude and conditions you're shooting in.
Admittedly, the appearance of UV filters and Sky 1B verse Sky 1A is less warm.
Good point about image degredation. even some 'drop-in' filters designed specifically for some long toms also affect quality, as found with my 300mm 2.8
However, I fitted a cheap filter to my 180mm 2.5....and the difference between it and the B&W one fitted now is marked!...
Yes, spend money on nice quality filters if you're going to use them
