I wouldn't dye a Coach bag.

No. It’s possible, but you’re more likely to ruin a nice bag than get a great result. Coach leather is usually treated with finishes that don’t absorb dye uniformly – you’ll end up with blotchy color that bleeds onto clothes.

If you’re dead set on trying, use a professional leather dye like Fiebing’s or Angelus, and only on uncoated, full-grain leather. Even then, expect to reapply and seal with a finisher. You’ll lose the original patina and resale value completely.

Better to sell it and buy the color you actually want.