Is there a graph starting from the 1950s?

https://www.lyrebirddreaming.com/post/el-ni%C3%B1o-isn-t-an-...

Looking at the graph left me wondering just what it means exactly. I'm not well versed in statistics so "the standard deviation is 3.5°C" doesn't mean much. Also, what's up with that other line going down to -3.5°C? And what do the colors mean? In the sense that I'm not sure whether a darker blue means closer to or further from today.