Hi guys. i have tried one of your expressions:

iff( rownumber(nothing) mod2, "blue","green")

i have a two groups and in the details again have grouped by three fields so that i can get sum for same kind of items. so i have applied this formatting to the details row but when i see the report it is showing two rows same color and again one row different and again two rows same. i dont get to know what is happening...