I believe sugar starts to turn amber around 320*. It starts to brown around 340* and burns at 350*. You might try switching from brown sugar to turbinado sugar, lowering your temps to 325* and tenting with foil when it starts to turn golden. Just be sure to keep an accurate temp on your IT for safety.
RUDEMIX - Klose 20X40 BYC, Custom UDS - illegitimi non carborundum