奇遇判定ならIfよりSelect Caseで分けると楽かな

Dim cngRng As Excel.Range
Set cngRng = Excel.Application.Range("A1:E20")
'範囲から上一列を除外
Set cngRng = cngRng.Offset(1, 0).Resize(cngRng.Rows.Count - 1, cngRng.Columns.Count)

Dim colorNum As Long
Dim r As Excel.Range
For Each r In cngRng.Rows
Select Case r.Row Mod 2 '行番号を2で割った余り
Case 0
colorNum = 1 '1=Black
Case 1
colorNum = 6 '6=Yellow
End Select
r.Interior.ColorIndex = colorNum
Next r