If you really wanted to make something exact, you could always make a stencil out of good masking tape. If it's pressed down really well, and you have a really fine scratch pattern in your blade, I don't see the mustard bleeding through. You could warm the blade up, do mustard for the grey/brown colour, let it sit. Clean it off and set it with mineral oil for a day or so. Follow that up with a nice red meat patina, set in between your mustard pattern and you'd get a great blue and grayish, interwoven look to the blade.