Density on the 2D plot

Hi,

is there any tool for visualization that could display density of the population on the 2d plot?
I have 2d principal components space for a table of molecules (2 millions of structures), and it's almost impossible to visualize all of them as dots just because of picture resolution and rounded pc values (so, there can be 1 molecule per pixel and 100 molecules per pixel). So, if there are any tricks to 

1. split colours of dots by column value and
2. distinguish abovementioned pixels hiding 1 and 100 dots by, for example, different brightness/intensity,

I would be grateful if anyone revealed them to me.

Thanks in advance and have a nice day,

Lana.