Thank you for the feedback.
After some last minute tinkering, I have improved the framerate by reducing the droplet count from 2001 to 1001. There is also an improvement to the colour calculation which makes it much more gradual, improving the realism.
I also added a picture. Maybe I should have called this "Rainbow Geyser". Is it too late to change the name of the entry?
If you squint your eyes a bit (or blur your vision slightly), you can almost see a rainbow.