Hello John,
Data Graphics are shapes based on masters in a very similar way to standard
shapes. As such you can edit shape instances or the masters themselves.
Right-click on a Bubble callout Data Graphic master in the drawing explorer
window and select Edit Master Shape.
This opens the Master editing window where you can view the respective
master shape and its shapesheet (by select the master and then clicking
Window/Show ShapeSheet.
Witin the shapesheet you'll find the Bubble callout's fill is set to accept
an applied theme colour and use 'Tint' and 'Tone's (shapesheet functions) of
that colour thereby giving a complimentary fill to the one applied to the
shape. if you're happy with the shapesheet then you'll be able to track the
cell references that include a number of User cells into the bargain.
A great place to start, however, is the Visio Insights blog that has covered
Data graphics in its last four posts:
http://blogs.msdn.com/visio/default.aspx
Best regards
John
John Goldsmith
www.visualSignals.co.uk