How do I change the color of NEW particles only? (CASCADE)

I have a stream of liquid and I want to change colors but only of the new particles, not the ones already in the air.

Set a color property based on a curve that uses age-of-emitter as input.
Typically, you will copy this property out of the emitter.
You can also drive the emitter color (to copy into the particle on construction) using a custom value that you can set from your code.