plotting PCA Noise Band

[tpgkevin]

I'm currently trying to plot out PCAs similar to phy in the featureview and I've gotten it mostly down. However, I do not know how the noise band (gray dots in phy) are picked. I have tried looking through the code and while I have found the line of code that gathers the background data, I still do not understand how it is choosing those points. I'd appreciate any help on the matter.

Thanks!