Change the background color in the properties of the row to an expression.

=IIF(RunningValue(Fields!YourField.value,CountDistinct,Nothing) Mod 2, "Beige", "White")
=IIF(RowNumber(Nothing) Mod 2, "Beige", "White")

or add the following custom code in the report properties (this version works well for Matrices)

Private Alt As Boolean

Public Function CandyStripe(Optional ByVal NewRow As Boolean = False, Optional ByVal OddColor as String = "Beige", Optional ByVal EvenColor as String = "White") As String
'------------------------------------------------------------------------------------------------
' Purpose:  To candy stripe the detail rows of a report
' Example:  Fill.BackgroundColor = Code.CandyStripe()
' Note:     The first column needs a parameter of "True" passed in example: Code.CandyStripe(True)
'------------------------------------------------------------------------------------------------
	If NewRow Then 
		Alt = Not Alt
	End If
	
	If Alt Then
		Return OddColor
	Else
		Return EvenColor
	End If

End Function
References:
http://disgone.com/2011/01/24/zebra-striping-in-sql-reporting-services/
https://code.msdn.microsoft.com/SQL-Server-Reporting-SSRS-50c4d06b