This node can be used to apply colors from a texture map across instanced objects. This node is used in conjunction with Scatter transform where the scatter will have an instance ID (ie. each block instance will have a unqiue instance ID). Please refer to https://render.otoy.com/forum/viewtopic.php?f=33&t=62395 for for details.
So in summary, if there are 5 occurrences of a block instance, you could have an Instance Range with a max id of 5, feeding a Mix materialUsed to mix any two material types. to get different colors on each block instance.