Patina color in cotton filter

[cornsqueezer]

Ok here goes I've read alot trying to get my answer and haven't found it so far. My question: is normal to see patina color in your filter? I use cotton to filter my alcohol with and it gets a slight patina color during the run. I didn't filter the foreshots(2 oz. or alittle more @ 2 gal beer) cause I was going to trash them anyway. what goes in the jar is clear as a bell. I do clean and scrub evetything except the coil but I flush it with water and then soak it with baking soda and water mix( thought maybe that it was acid that was causing it) I did read where Rad1407 said not to clean and scrub cause it would just patina again so from now on I'll just flush out with water if that is good enough. just so ya'll know I am running a 12qt ss pot with 1" collumn 24" tall, 1/2" arm 24" long and 10 ' of 1/2"o.d coil in 5gal bucket its small and takes a while to run but it will have to do for now ( still learning) any info will help