On the example Image, all particles are colorized by a Red
Colorize then masked may an Age Mask.
This can also be achieved with a lot more options by using a
Function set as Age.
This mask allow to use
Field or
3D Modifier only on a defined period of a
Particles lifespan. If you want for instance for gravity to affect only dying particles, just set a function mask as Age over a
Gravity and make it work only on the end of the lifespan. Here is an example: