Recently, when I used a B&W UV filter on my Leica Elmarit 28f2.8, I noticed a different behavior on the lens. The pictures do not appear as sharp as before because when I first bought it I was using the lens naked as I could not find a 48mm filter for it. A kind CS member here gave me a 48-58 step up ring and I began to use my 58mm B&W filter on it and began to notice the difference in clarity and sharpness. I did a series of 6 pairs of shots, each pair, one with and the other without the filter. There and behold, you don't need 100% crop to tell the difference. Since then, I only use cheap filters to protect my lens. Of course, N, CPL and GND filters are different.
yeah, good filters are able to replicate nicer colours and sharpness... best is remove filters during shoots...