Change font colors for choices in drop down list on Adobe PDF using Adobe Acrobat Pro.

You can use this as 'Validate' script of dropdown field:

if(event.value == "VERY LOW" || event.value == "LOW")
event.target.textColor = color.green;

else if(event.value == "MINOR")
event.target.textColor = color.blue;

else if(event.value == "MODERATE")
event.target.textColor = color.yellow;

else if(event.value == "SERIOUS")
event.target.textColor = ["RGB", 255/255, 136/255, 0/255] ;//orange

else if(event.value == "HIGH")
event.target.textColor = color.red;

When you make a choice it will change to a specific color but if you go and make another choice, while you are choosing all choices will have that same color if it's fine with you leave as it is, but if you wish for them to have black color while selecting use this as 'Mouse Down' action of same dropdown field:

event.target.textColor = color.black;