Go to the BP_FloatingNamePlate_02 and create a new macro in the My Blueprints panel call it IsInGuild then copy the image below.

Next create a new variable called GuildColor and set its variable type to Slate Color. You can set the color in the details panel to whatever you like. The default color Hex Linear code is 3CB8FFFF

Add the highlighted nodes shown in the image below, location at the top of the image.

Now repeat the steps in the BP_FloatingNamePlate_01.