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: