It's normal for sweet potato bread to turn green.
Sweet Potato Bread turns green because sweet potatoes contain flavonoids which is a type of anti oxidant and also sweet potatoes contain pigments which when those flavonoids and pigments are exposed to air the color can change to green.
Your sweet potato bread is still good and safe to eat even when it changes to a green color as it's not mold.
Unless you see actual mold spores then it's okay to eat the sweet potato bread that has turned green.
I sometimes have sweet potato bread that turns green and I thought at first it was bad but it's actually just because of the sweet potato bread being exposed to the air.
When those pigments in the cooked sweet potatoes are exposed to air they turn green which can also happen to just cooked sweet potatoes that are left out in the air for awhile.