Here is what you gotta do:
Add 2 conditions to the conditional formatting section of your repeating section. Use these two equations. The Mod operator (mod, %) really just gives you a remainder as an output.
5 mod 2 = 1 5/2 has a remainder of 1
6 mod 3 = 0 6/3 has a remainder of 0
Use these two equations.
1. number(position() mod 2) = 0 - then set the shading to what ever color you want.
2. number(position() mod 2) = 1 - then set the shading to what ever color you want.