I don't know if you ever got a response to your question, but my best guess based on my limited elephant ear knowledge (as a new ee fanatic) is that they are getting sun at the hottest part of the day (afternoon) and that is burning them. Try them in a different location with more shade.

I also live in Florida zone 9b/10a and have this same colocasia. I think LaLennoxa is spot on. This colocasia wouldn't mind morning sun, but afternoon Florida summer sun will fry them. I'm surprised they look as good as they do. Katie, try a few in another location with only morning sun and see if they don't look much better. They will likely go dormant during winter, but starting in spring it might be a good plan. They can be beautiful plants!