Comparing curves and generating a qualifying metric

I want to compare the frequency response generated by two analytical models (Red and Blue) with that of the reference model (Black).

As you can see, the Red curve does a better job of capturing the resonances than the Blue one. I would like to qualify and quantify this improvement in the form of a metric, perhaps an overall percentage improvement, or other such quantities.

In-depth answers will really help, as I am quite inexperienced in the Mathematics involved, and in making such comparisons.

I really appreciate the help.

Cheers! :wave: