want to make it so that on an event the actors colour changes to a different one
You should use dynamic material instance.
WTF Is? A Dynamic Material Instance in Unreal Engine 4 - YouTube follow this tutorial and you will be ready to go!
Matt Wadstein is great. Also, this video from Epic is the one I learned from. It’s a bit old but you should be able to get around the minor differences between UE4 versions.