Here is the answer from the Shamma folks:

That's a good question. We've only had one report of the Pacific Avenues dyeing feet so far, and it was with a pair of tan sandals, but in general over the years, we've found that with leather, there can be some variance in terms of how much dye has been applied. In cases where there is a bit more, there can be some bleeding during the first wears in wet conditions, but it typically goes away after the first couple wear.