That's why you should soak the wood for at least a few days. I soak my bigger pieces of driftwood for at least 2 weeks changing the soaking water every few days. Once it's in the tank Purigen and extra water changes should clear up what ever colour it leaks.
I just use filtration. If you can adapt some type of micron filtration around 2-10 micron that will catch the tannins. I use packed polyester batting and white felt and then a 2micron sock on my sump and the tank is filled with wood and I have never seen a tannin. But the filters turned brown and clogged for the first few days after the wood was put in. So I had to rinse the filters daily at first. Now after a few months I have to wash them out once a week.
Soak in boiling hot water for two weeks and you should be good to go. Becareful not to burn yourself when doing this. You can soak it in cold water too but it'll take you longer. The longer you leave it soak in water before using in the tank the less the tannins will leach out.