Unable to customize the heat map color ramp in ArcGIS Online

Description

The heat map color ramp in ArcGIS Online is not customizable, unlike the ones offered in ArcMap and ArcGIS Pro. In ArcGIS Online Map Viewer, limited options of pre-configured heat map color ramps are available by clicking the Symbols icon in the Change Style setting, as shown below. There is no option to customize the RGB (red, green, blue) or Hex values in the Change Style setting.

Cause

This is a known limitation in ArcGIS Online. The RGB value of a heat map color ramp is not customizable in ArcGIS Online Map Viewer, unless configured through the ArcGIS REST Administrator Directory page.

Solution or Workaround

The image below shows a pre-configured heat map color ramp by clicking the Symbols icon. Use the following workaround to customize the heat map color ramp in ArcGIS Online Map Viewer:

Note:
To perform these steps, log in with administrator credentials.

1. In ArcGIS Online, create a heat map from the desired point layer, and click Save Layer. This creates a feature layer in the My Content page.
   
   
    
2. Open the item details page of the heat map feature layer, and click Publish. This creates a hosted feature layer in the My Content page.
   
   
    
3. In the item details page of the hosted feature layer, navigate to the Layers section, and click Service URL.
   
   
    
4. In the heat map layer's ArcGIS REST Services Directory URL, insert admin between the rest/services portion (as shown in the image below), and press Enter on the keyboard.
   
   
    
5. In the ArcGIS REST Administrator Directory page, scroll to the bottom of the page, and click Update Definition.
   
   
    
6. In the Update Layer Definition page, press Ctrl + F on the keyboard to open a search bar. Search for drawingInfo. The drawingInfo parameter lists the RGBA values of each heat map color stop in the format of red (R), green (G), blue (B), and alpha(A). The alpha value controls the color opacity.
   
   
    
7. Change the RGB values as desired, and the alpha values if necessary. To determine the RGB values, use the RGB Calculator as reference.
    

   Note:
   The alpha values range from 0 (fully transparent) to 255 (the default maximum value). Changing the maximum value to more than 255 is possible, but does not show any effect on the map.
   
   Ensure the alpha value of the first color stop is set to zero. Setting the alpha value of the first color stop to other than zero fills ArcGIS Online Map Viewer with a background color, as shown in the image below.
   
   
   
   Ensure the alpha value of a color stop (other than the first color stop) is set to other than zero. Setting alpha values of color stops to zero creates hollow rings, as shown in the image below.
   
   
   
   

    
8. In the search bar, search for lastEditDate. Change the lastEditDate value to " ".
9. In the ASync field, select True.
10. Click Update Layer Definition.
    
    
     
11. Open ArcGIS Online Map Viewer and refresh the page.
    
    The image below shows the customized heat map color ramp according to the desired RGB and alpha values.