LP Filter and Star Colour calibration?

Based on that algorithm that seems to be a good calibration yes. The data points are brought closer to the optimal diagonal line which is the expected trend. You can tell that the stars are nicely blue-ish and orange as expected and the H-alpha signal is correct as well. You can play around a bit with that reddish color and make it slightly more pink (which technically is more correct or redder as that's usually perceived as being nicer). In the end there is only the technical correct color belonging to the actual spectrum of the gas and stars, but there's no real "best" color as most is personal preference.

Great, thanks for the feedback.

So in a nutshell if I understand the graph methodology, I want the majority of stars to be along the diagonal, and around 90% or so to be positive, with the remainder negative (blue stars)?