Nodes cannot be turned off.

Hi,
I don't know what has changed in my settings but if you look at the tree to the left, you will notice it is purple, but it's not, it's a duplicate of the larger one and resized. There are so many nodes that it obscures the image. Can't edit the colour if I can't see it, unless I enlarge everything 100X.  Don't have the foggiest idea of what term to type in the Help menu.

Thanks in advance