@FrankTheTank Thanks for your nice words, glad the code worked (at the moment from a laundry shop, currently about to leave the Rockies).
My goal with Chartaffair is to 'empower' especially small traders - who might not be so quant-savvy - with useful and high-quality tools. And I will add whatever serves this purpose.
Since you asked: Heatmaps have been asked for a lot for. So yes, of course I will add a heatmap section and more useful stuff after returning (in fact they are practically ready, not much is missing. What I can see already is that despite the large amounts of data page load times will be very good - just like the rest of the site has been so far).
I can see the issues you point to. It should be possible to change to median return and get the colors more defined. I need to add that the heatmap you can see now on the page, however, is basically only a toy to give a first impression, nothing more.