Finally, I found how to do it with the change of color for the material and it much simplier that I fought (but when I see the the time in took me, it’s a joke :p), you have to:
• create a HUD with the 3 sliders (Value, Desaturation, Value)
• create custom events from these sliders
• create a Material Parameter Collection with 3 scalars output
• go back to the HUD and connect Exec/Value output to a “Set scalar parameter value” and in the “Collection” entry, select your Material Parameter Collection
and voila !