Blend function in scatter or scatter3?

When zooming out from a large coloured point cloud (each point in the cloud has a specific colour representing a property, the pointsize is 1 as the alpha) in either scatter or scatter3, the colours change (become darker) as more than one point occupies a pixel. Clearly there must be a blend function to combine the colours of these opaque points. Is it possible to find out what this function is?