Select the chair in the level, then in the Details panel under Materials, click the Browse To (Magnifying glass) icon.
The Material used for the chair will be highlighted in the Content Browser, Double-click on the M_Chair Material to open it in the Material Editor.
Mouse-Wheel Down to zoom out and find the node with the orange square and click on it, then in the Details panel, click the Default Value bar.
In the Color Picker window, click and drag the orange color (in the yellow box) to the Save Color bar to save the color.
We will use this later as now we have a reference to the default color of the seats.
Close the Color Picker window (no need to save) and close the Material as well.
In the Content Browser, Right-click on the M_Chair Material and choose Create Material Instance.
A Material Instance of the Material will be created in the Content Browser which we can edit. You can leave the default name.
Select the chair in the level, then select the M_Chair_Inst in the Content Browser and in the Details panel, click the Arrow icon.
This will assign the Material Instance to the chair.
Open the Matinee Actor (the Matinee assigned to the chair) and click on the ...Material Param (Material Parameter track).
In the Details panel on the right, click the Add icon.
Back in the Content Browser make sure the M_Chair_Inst Material Instance is highlighted, then in Matinee, click the Arrow icon.
In the Param Name field, enter ColorSeats (as this is the name of the node in the Material from step 3) that we will alter.
Click on the Material Parameter track and press Enter to add a keyframe at 0.00, then move the Time Bar to 2.00 and add another keyframe.
Right-click on the ending marker and choose Move To Longest Track Endpoint to reduce the Matinee length to two seconds.
Right-click on the first keyframe and choose Set Color, then from the Color Picker menu, select the bar at the top to assign the default chair color.
Right-click on the second keyframe and choose Set Color, then from the Color Picker menu, select any color other than the default color then close the Matinee.
This is the color the chair will blend to when the player approaches.
In the World Outliner, select the Matinee Actor, then from the toolbar select Blueprints - Open Level Blueprint.
Inside the Level Blueprint Event Graph window, Right-Click and from the context menu, select Add Reference to MatineeActor.
Minimize the Level Blueprint, then in the World Outliner locate and select the TriggerBox1 so that it is highlighted.
Re-open the Level Blueprint and in the Event Graph, Right-click and select Add Event for TriggerBox1, Collision then Add OnActorBeginOverlap.
This event will execute when an Actor (our player in this case) overlaps the trigger box.
Repeat the previous step, however this time select the Add OnActorEndOverlap.
Click-and-drag off the out pin of the MatineeActor node and release, in the context menu search for Play, then select Play from the menu.
Repeat the previous step, however this time search for and select Reverse.
The Matinee should be hooked up to both a Play and Reverse node.
Click-and-drag off the Execute out pin of the OnActorBeginOverlap node and connect it to the in Execute pin of the Play node.
Repeat the previous step, however drag off the OnActorEndOverlap node and connect it to the Reverse node.
Click the Compile button located in the upper left of the Blueprint window.
Close the Blueprint, then click the Play button from the main toolbar to play in the editor.
By default the chair should remain orange, however when you get close to it, it should blend to and change to the color you selected.
When you move away from the chair, it should blend back to the default color.