Using keyword instead of text for field color

Getting an error message on Kibana console 6.4.2
"error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [color] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."
      }
    ]

300_Aggregations/20_basic_example.asciidoc

@@ -52,7 +52,7 @@ GET /cars/transactions/_search
     "aggs" : { <1>
         "popular_colors" : { <2>
             "terms" : { <3>
-              "field" : "color"
+              "field" : "color.keyword"
             }
         }
     }