I've been using Kenrico pads from Japan which supposedly are some of the best quality. I've used the Green pads and the Blue so far. My experience is that I have not yet noticed too much (has been able a week of usage), except my heels seem to be quite a bit drier, and a couple days I've woken up with a slight headache (although that may be caused by other things including lack of sleep!). When I take them off, they are a light light brown color and appear to be no different than what the natural ingredients inside would probably look like normally. I will try the 'soaking in water' test to see if they turn the same color.
For me, what I see isn't even so much important as how I feel, and I have yet to notice any difference in how I feel. I do have some reservations about how these pads work and their effectiveness, but I will give it some more time. I'm thinking about sending some in for testing for toxic materials, however I cannot find anyplace other than the one selling them, and that of course would be conflict of interest ;)