color-coded indicator icon

hey duc_resolvevn ,

The Indicator Widget has a dedicated API, as provided in the following official link and examples shared in the following community post.

please find a sample Indicator widget script of customizing the secondary indicator and add an arrow symbol. 

widget.on('processresult', function(w, e) {

 var options = {

 secondaryValue: {
 fontFamily: 'Helvetica, sans-serif',
 fontWeight: 'bold',
 color: 'grey',
 fontSizes: {
 big: 20,
 medium: 15
 }
 }
 };

 
 if(e.result.secondary.data >= 0) {
 
 e.result.secondary.text = '▲' + e.result.secondary.text;
 options.secondaryValue.color = '#00FF00';
 
 
 }
 else {
 e.result.secondary.text = '▼' + e.result.secondary.text;
 options.secondaryValue.color = '#FF0000';
 }
 
 w.indicatorInstance.setOptions('numericSimple', options);

});

Alternative solution can be using Blox which provide ability to add more Indicators and customize it. 
in the Blox Template, please refer to the Stock Market which provide an example with conditional formatting and image.

FYI DRay 

best regards