I hope this doesn't come off as bad, but I see people giving advice here that is counter to the advice of experts and testing and uses, hate to say it, bad logic. I feel I have to risk that.
Here's some data on climbing ropes and magic markers. If a magic marker can do this to a climbing rope, then spray paint is likely worse. Dynamic ropes are made of nylon, just like saddle webbing.
Also, I have to point this out so that others do not read other posts and get hurt:
Stating "I spray painted my saddle and didn't die" should be as compelling a reason to follow suit as "I got really drunk and drove home and didn't wreck". It is an anecdote, not data and ignores probability.
This has been brought up here before and many people said "don't paint your saddle or other life support, especially with anything containing a solvent". So, I don't think this thread is reflective of what folks would say here if all members were polled.
A solid color saddle in an earth tone that contrasts your outer wear helps to break up your outline and is not a concern for a deer detecting you at all. In fact, if you had sections of cloth, like a saddle, sewn all over your clothes randomly, it would probably be really good camo.