Are they designed to go an odd colour on puporse? 
As a little experiment to myself when out the other night, I nabbed a filter off a mate and while half the people at the table lit up, I poked the filter in my mouth and breathed through it. This wasn't the easiest thing in the world but y'know
After about 5 minutes or so of breathing through it, it had gone a horrible nasty yellow/brown colour, now I know this is meant to happen but I was slightly concerned that it was discoloured so much just by 'passive' smoking.
So I was wondering if they perhaps are designed to change colour more than they really would to give the impression they are filtering crap out better?
...if you see what I mean.

As a little experiment to myself when out the other night, I nabbed a filter off a mate and while half the people at the table lit up, I poked the filter in my mouth and breathed through it. This wasn't the easiest thing in the world but y'know

After about 5 minutes or so of breathing through it, it had gone a horrible nasty yellow/brown colour, now I know this is meant to happen but I was slightly concerned that it was discoloured so much just by 'passive' smoking.
So I was wondering if they perhaps are designed to change colour more than they really would to give the impression they are filtering crap out better?
...if you see what I mean.