As of early April, 2025, this appears to be an issue. I think this may have been introduced in the Feb 2025 ArcGIS Online update.
We saw this same issue when creating gauge on a dashboard, with the gauge showing only "error."
On existing dashboards, gauges were working as expected, but if we changed the Band color of the active threshold, that is, the one that includes the current value, the gauge would immediately break.
Looking at the dashboard in ArcGIS Online Assistant, viewing the JSON, it looks like a change was made as to how the colors are being stored for the various thresholds, from hex code to RGB.
For the existing gauge, the previous hex code json:
"colorThresholds": [
{
"threshold": 0.3,
"color": "#ff0000"
},
{
"threshold": 0.6,
"color": "#ffee00"
},
{
"threshold": 0.99,
"color": "#26ff00"
}
]
and when we change the color for the active threshold (the 2nd threshold) and save, the json then looks like this:
"colorThresholds": [
{
"threshold": 0.3,
"color": "#ff0000"
},
{
"threshold": 0.6,
"color": [
255,
187,
0,
255
]
},
{
"threshold": 0.99,
"color": "#26ff00"
}
]
Using ArcGIS Online Assistant, you can change the element to use a hex code and the gauge will work. We replaced the RGB element in the colorThresholds element with a hex code value for the same color. This can also be done on a new gauge after saving the dashboard and modifying the colorThresholds section in ArcGIS Online Assistant. As you configure the gauge, grab the hex codes of the Band colors to apply over in ArcGIS Online Assisant.
In this example, replace [255, 187, 0, 255] with "#ffee00" (include the double quotes for the hex code)
Of course, everytime you want to adjust the color, you'll need to do this operation in ArcGIS Online Assistant as a followup.
