Hi,
I have modified the formula for User.LineColor for both Rough Wire and Finish Wire so that Control wires show as purple and not grey. Place the attached Wire and Cable.vss in your C:\Documents and Settings\All Users\Application Data\D-Tools\SI5\Visualizations\Stencils folder and you should be OK.
Take a backup of your current Wire and Cable.vss before replacing it with this file in case of any problems.
Wire and Cable.zip
Naresh