The feature itself looks good, but the alpha handling here seems suspect - writing a ColorBgra with straight alpha into the Cairo surface is definitely incorrect since it expects premultiplied alpha.

Ideally this would work with premultiplied alpha all the way through to avoid future work for #1553 (e.g. ColorBgra.Lerp() can be used for the blending)

I have to admit to a bit of ignorance on this; not enough to ignore what premultiplied alpha is, but I would need some focused time to construct my mental models and ensure that I'm blending the colors correctly (and using the right methods, if they exist, or create them if they don't).

For now I just made the points black, and I could handle the blending in a future pull request.

Thanks, that sounds fine for now - I've added a note to #1553 about fixing RandomColorBgra() to create colors with premultiplied alpha which I think is the main issue for these effects, aside from the straightforward changes like replacing color.ToColorBgra() with color.ToColorBgra().ToPremultipliedAlpha() (eventually the conversion should always do this for you)