Object Properties node allows to change instances properties like assigned material, reference object and color.
Usually Object Properties node is used together with Separator node for replacing properties of some part of instances, or it can be used independantly for changing color of all input instances.

Replace object replaces reference object for input instances. New reference object requires a new collision sphere setup similar to Scatter node.
Replace material replaces assigned material for input instances.

Modify color allows to change instances colors to fixed one or with a texture. Instances colors are used for viewport display or for rendering by connecting FStormObjectColor texture to a material.