Hi Anunciada,
If I spotted it correctly, he uses a Random Effector to set Weight for the next Effector to use. The second Effector was then only there to set the color.
However you like to do it, the first step is to set the Voronoi> Object> Colorize Fragments… to none.
In the files below, I have used two ways to get to monochrome colored Fragments.
The first example [01] uses an Effector to set to Parameter> Fields Color. Then a formula effector uses the ID that each clone has to produce a value. The count is the overall number of Fragments here. So with ID/count, the result is always between 0 and 1. Which sets the color. The value 0 provides white, and the value 1 gives the full color that is chosen.
The second example [11] uses the gray-value that results from just the numbers as above, but no Fields object is used here. The colors are then produced in the Material, while the MoGraph Color provides these gray (or black to white) values, and the Colorizer translates it to any color you like to have, based on the brightness to gradient translation.
Project files
https://www.amazon.com/clouddrive/share/XoWLZLf50SzYlovMOUeANDRtaFnI2XT1wclnG9ivpqd
I hope that gives you what you like to have.
My best wishes, stay safe, stay healthy.