It is possible to define how a Charts Line and Marker will be represented by creating the Graph Series Styles within OpenGround Cloud.
Once the styles have been created they can be used within the Excel Extension.
After setting up the reports data and inserted the appropriate chart into the template click the Charts Icon from the interface. You will notice the field Style selected from the image below.
This field is used to source the marker and line styles from where they were defined in OpenGround Cloud. The below example will illustrate the style defined against Location IDs however you could have chosen a picklist to source from as there are many options available for use.
Referring back to OpenGround Cloud you will see the style matches with the graph output.