Actually Spirits CAN proc yellow believe it or not. I was with a few friends fighting the Penguin NM out in Abyssea and we needed Freeze to proc and I had whipped out my Spirit and it did Cast said spell and proced. It was sheer luck and I wish I could have screen shotted it but I keep forgetting how to do that since I switched to PC.
I will keep saying this like I said in another thread, I think Spirits mechanics should be more like the Automaton's, even though the Automaton's AI is bad the Spirits are faaaar worse and at least the Automaton casts every 30ish seconds.
Automatons have the ability to see a Monster's health and determine what spell to use on it, I think a Spirit should. A Automaton See's its Master as well as their Party in low Health and it cures, I think Light Spirit should do that. Also Automaton have spell priory (which should be changed) and it is I think it was Na-spell > Heal > Enfeeble > Nuke and I think Spirits should work the same way.
Sorry edit, it was Freeze on account we didn't HAVE a BLM and that's what spell we were missing besides Blizzaga III