For this mask to be effective,
Particles
Simulate a particle system
Read More
needs to have a changing velocity. For this apply some
Field
Defines a force-field in 3D space
Read More
over them.
On the example image, all particles are colorized by a Red
Colorize
Colorize all the vertices of the geometry uniformly
Read More
then masked by a Velocity Mask.
Some modifiers, like
Colorize Function
Colorize all the vertices of the geometry using a Color Gradient and a 3D Mask
Read More
directly have a mask inside of them.