Changing the backgrounds colours and images.
Configuring Background Colours, Sizes and Graphics
The SharePoint Org Chart has a number of built in background styles and colours that can be set for each box on an organisation chart.
Often these built in styles are sufficient but if required they can be changed. This guide explains how to change those colours and also how to define custom background colours.
This guide also explains the difference usage scenarios between the Graphical and CSS background options that are available.
Changing the background colour

In the Org Chart web part, navigate to Chart Items within this configuration section the Background colour is used to select the desired color.
Changing the Size of the Org Chart Box

The size of the chart box can be set by adjusting the Size (circled in red) property in either the Chart Items or Assistant Items configuration section.
Defining a Custom Background Size

To set a custom background size enter the size in pixels into the Custom Box Height and Custom Box Width properties.
The image below shows a chart with the Custom Box Height set to 50 and Custom Box Width set to 200
Changing to CSS Background Mode.

The Org Chart supports two different modes for drawing the background, Graphical and CSS. Choose the mode you wish to use by selecting the Background type in the Look & Feel configuration section