Ok, I see what you want now.
Option Explicit
Sub ColorRows()
Dim LastRow As Long
Dim LastCol As Long
Dim i As Long
LastRow = Cells.Find(What:="*", After:=Range("A1"), LookIn:=xlValues, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row
LastCol = Cells.Find(What:="*", After:=Range("A1"), LookIn:=xlValues, _
LookAt:=xlPart, SearchOrder:=xlByColumns, SearchDirection:=xlPrevious).Column
For i = 1 To LastRow Step 2
Range(Cells(i, 1), Cells(i, LastCol)).Interior.ColorIndex = 4
Next i
End Sub