Couple of things...
First, you are several major updates behind. 12.2.1.5 is the current version and they've introduced a number of new features in 12.1 and 12.2 that you are missing out on as well as many bug fixes.
It won't help your current problem (which I'll explain in a minute), but you should definitely update.
Secondly, if you're new to AE, you need to start here. I'm very serious. You need a solid foundation in the basics or you will be frustrated.
Third, and pertinent to your issue, you need to understand how the Curves effect works. Your Audio Spectrum effect is set to create itself as pure white. You can't change the color of pure white with the curves effect the way you're hoping to. Make the color a mid grey and you will then be able to change the color with the Curves effect. Again, I wouldn't recommend doing it this way with the adjustment layer, Curves, and all that, but if you must, that's how.