That's not scorched. It's a transfer of the yellow dye onto the white fabric, from the yellow fabric next to it, when the iron moved across the yellow onto the white. I had it happen to me once with a red dye onto a white fabric, and all my fabrics were prewashed/shrunk before I cut anything. The problem is in the manufacturing of the offending fabric. It's not your fault. There is a name for this, too, which I can't think of right now (something like crackling or crazing ??). When it happened to me, I put a tiny bit of liquid soap onto a clean damp washcloth and rubbed it out, then rinsed it. But if I was careless with which way I moved my iron, it would happen all over again, even in the exact same place. Big bummer, because the quilt was a gift. But after I got all the red smears out, I decided it shouldn't be a problem, because I don't expect the recipient will be ironing her quilt anytime.