What shaman said. Fluorescent orange absorbs UV and emits orange light, that's why it's brighter than plain old orange. Very little if any UV gets reflected back to the deer. Also deer don't see orange very well, looks like a muddy brown to them. See NY DEC for pictures and a short explanation of both points.

The key elements in human thinking are not numbers but labels of fuzzy sets. -- L. Zadeh

Which explains a lot.