Hi Cindy,
How did you create your features? Did you use the Shortlist Builder in ArcGIS Online? Did you use a feature service? Did you use a CSV file? It all depends on your data source.
I started with the Shortlist Builder and edited the web map JSON using the ArcGIS REST API. The Shortlist Builder creates a web map with a shortlist layer defined by a feature collection. A feature collection is just a representation of a feature class that contains a schema and the features. In the schema is a "fields" property where the fields are defined. You need to add the following field to this array:
"fields": [
...
{
"alias": "Color Index",
"domain": null,
"editable": true,
"name": "color_id",
"type": "esriFieldTypeInteger"
},
...
]
If you want to do it this way, you can use the ArcGIS Online Assistant to view and edit the web map JSON. You should make a backup of your web map before doing this. Also, IE 11 has given me trouble with editing JSON, but Google Chrome works with the ArcGIS Online Assistant. Basically, you need to add this field to the fields array, which defines the fields for the shortlist layer, and then you will need to add "color_id" to each of the features themselves. After that, you need to duplicate all of the features for the All tab, update the necessary fields, and then move on to the source code.
If you are using a hosted feature service, it should be pretty easy. All you should have to do is add the field in ArcGIS Online or Portal. A long time ago, I tried replacing the shortlist layer from a CSV file and it wasn't too difficult. I think I just deleted the shortlist layer and added a new layer from a CSV file. The file had to have the required fields, but you can get those from the web map or the documentation.
If you are having trouble, I can probably help you with this provided that you have the web map shared publically. I can copy it to my account, modify it, and then you can copy it back. Either way, let's start with where your features are located.
Thanks,
Nathan