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That is a graft-line. I have bought several graft blanks. I thought they were cool when I was younger. The heart wood is dark on the English side but the sap wood and heart wood is very blond looking. The fore end looks exactly like the butt stock. Claro on one end, dark graft, heart wood, graft line and then blond English wood. A lot of orchard English is blond looking. Dark color seems to be in the minority. Most likely the trees were cut to soon for them to mature and have lots of heart wood. I expect they were sent hundreds of stock blanks and this one was at the graft line from a orchard tree. Since they paid for it they used it. I have only seen a few graft-line blanks used on custom guns, never a field grade gun. This is what a lot of orchard grown English wood looks like. That is the English part that grow above the graft. They use Claro root stock to graft the English to.