Direct Styling

You can add html on the Jira Screen (use the Developer mode or look at the workflow i Jira to find Transaction Ids):

<style>
/* Close */
#action_id_251 {background-color: #ff0000; color: #ffffff}
/* Candel */
#action_id_201 {background-color: #ff0000; color: #ffffff}
/* Submit */
#action_id_11 {background-color: #00ff00; color: #000000}
#action_id_381 {background-color: #00ff00; color: #000000}
/* Start Deployment */
#action_id_311 {background-color: #00ff00; color: #000000}
/* Decline */
#action_id_21 {background-color: #00ff00; color: #000000}
</style>


Or You can add a Javascript the colors the buttons by button text:

<script>

// https://www.w3schools.com/cssref/css_colors.asp

AJS.$(document).ready(function(){

var elements = document.getElementsByClassName("trigger-label")

  for (var i = 0; i < elements.length; i++) {
  
    //alert (elements[i])
	
	switch(elements[i].innerHTML.toLowerCase()) {
  
  		case "close":
		case "close issue":
    		elements[i].parentNode.style.backgroundColor="CornflowerBlue";
			elements[i].parentNode.style.color="White";
    		break;
			
		case "cancel":
    		elements[i].parentNode.style.backgroundColor="CornflowerBlue";
			elements[i].parentNode.style.color="White";
    		break;
			
		case "resolve":
		case "resolve issue":
    		elements[i].parentNode.style.backgroundColor="LightGreen";
			//elements[i].parentNode.style.color="White";
    		break;
			
		case "submit for review":
    		elements[i].parentNode.style.backgroundColor="LightGreen";
			//elements[i].parentNode.style.color="White";
    		break;
			
		case "submit for authorization":
    		elements[i].parentNode.style.backgroundColor="LightGreen";
			elements[i].parentNode.style.color="White";
    		break;
  
  		case "set in progress":
    		elements[i].parentNode.style.backgroundColor="Green";
			elements[i].parentNode.style.color="White";
    		break;
			
		case "change priority":
    		elements[i].parentNode.style.backgroundColor="CadetBlue";
			elements[i].parentNode.style.color="White";
    		break;
			
		case "bounce to customer":
    		elements[i].parentNode.style.backgroundColor="LightSalmon";
    		break;
			
		case "assess issue":
    		elements[i].parentNode.style.backgroundColor="PaleGoldenRod";
    		break;
		
		case "bounce to customer":
    		elements[i].parentNode.style.backgroundColor="PapayaWhip";
    		break;
	}
  }   
});
</script>