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