All of the attempts below result in `ERROR 000358: Invalid expression` Any ideas on what I am doing wrong?

Attempt 1:

    def SelectLayer(val):
        print '"Att1 = ' + "'" + val + "'" + '"'
        arcpy.SelectLayerByAttribute_management('Source_lyr',
                                                'NEW_SELECTION',
                                                '"Att1 = ' + "'" + val + "'" + '"')
    SelectLayer('Red')

Attempt 2:

    def SelectLayer(val):
        where_clause = '"Att1 = ' + "'" + val + "'" + '"'
        print where_clause
        arcpy.SelectLayerByAttribute_management('Source_lyr',
                                                'NEW_SELECTION',
                                                where_clause)
    SelectLayer('Red')

Attempt 3:

    def SelectLayer(val):
        print "\"Att1 = \'{0}\'\"".format(val)
        arcpy.SelectLayerByAttribute_management('Source_lyr',
                                                'NEW_SELECTION',
                                                "\"Att1 = \'{0}\'\"".format(val))    
    SelectLayer('Red')