Actually, I'm doing this exact thing right now. Tressostar green tape, trying to match the forest green on my Heron. I'm using blond shellac flake. I have four coats on so far and the color is pretty nice. It's still lighter than the frame, but I'm not looking for an exact match.

As an aside, the Tressostar really annoyed me -- that stuff has always been difficult -- and being as I've decided to swap out my bar-cons for downtube shifters, I ordered some more tape. Vista brand, made in Japan, supposedly better than Tressostar and Cateye, but a bit pricey at $12 pair pair from Jitensha Studios. Just arrived today and the dark green is very, very close to the forest green on the frame. I think with a few coats of shellac it will be practically identical. I won't be using it for another week or two, but if the thread is still active at that point I'll write it up and add some pics.