This is a picture of what I'm pretty confident is coralline on the back wall of my tank the other day. Today it looks like it's a smaller patch and the color is much less vibrant. Did I lose my first chance at getting coralline algae in my tank?
Looks like coralline to me. And its growth might have been aborted for whatever reason.
But if you had one spot of coralline, it'll only be a short time before you see more.