You were perfectly clear.
Select rows 1 to 100 then Format>Conditional Formatting
Condition1>Formula is =MOD(SUBTOTAL(3,$A1:$A$2),2)=0 one color
Add............
Condition2>Formula is =MOD(SUBTOTAL(3,$A1:$A$2),2)=1 another color
You will get alternating row colors down to row 100.
one color
another color
one color...........same as row 1
another color...........same as row 2
etc.
Gord