#Material Instance Dynamic Solution
Instead of just switching materials on and off
you could also consider using a material blend, between the original material and the highlighted/affected material
or you could just dramatically change color and brightness or change a texture or something liek that
then you could grab the material instance and set the alpha of the material blend between 0 and 1 based on where the sphere event is in relation to them.
this would save you from having to change materials and store their values somewheres
you’d also be able to do checks on any stray actors whose materials were not set properly by iterating over actors and checking out the status of their material blend alpha (ie, it is 1 when it should be 0)
Rama