Most of the leaves on my tree are discolored. A sort of deep purple/gray. There are some leaves which are bright green and I assume they are new growth. This has been going on for a couple years now. It doesn't seem to be affecting the health of the tree, just unsightly. Also, it doesn't seem to bloom as much as before. See picture showing the affected leaves side by side with healthy ones.

Any idea what is causing this?

I am in south Louisiana and the tree gets sufficient rain fall and I have never fertilized it.