Hi
Create a running total based on the group use the below settings for Running total
Field to summarize group field
Type of Summary :Count
Evaluate for each record
Reset OnChange of Group
Once done Go to Details Section right click Select Section Expert then Click Color Tab in Section Expert and write the code below
if {#RTotal0} > 1 then
crSilver
else
crWhite
this will keep the first line in group with nocolor rest will be CrSilver,but if you have single detail line related to group ,that will also be in nocolor.
Cheers
Rahul