If you accept answer from a novice user…
Method posted by ‘realtime’ is (almost) what I need. I tried density_heatmap and imshow but couldn’t get satisfactory results.
I mean I think I know how to get there with mentioned two methods but few extra steps are required. With realtime’s method I get straight translation of values to color without bins and no need for manual mapping. Graphs from both ‘legal’ methods look quite different from what I expected, while ‘illegal’ get me right to where I wanted to be (almost 
).
That said… let me thank you for Plotly. I think… No, I’m sure! it is awesome! Thank you very much for it.