Thank you for the interest in NodeXL!
To reveal the columns that control the color of each edge, see:
NodeXL>Show/Hide>Workbook Columns>Visual Properties
To control the values of these columns without direct editing, see:
NodeXL>Visual Properties>Autofill columns
Select the "Edges" tab (its the default focus) and select the Edge color, opacity, style, or width and then select the data value you would like to map to them.
You may need to import the Vertex group ID into the Edges worksheet to achieve the result you describe. You may accomplish this via the Excel =VLookup() function.