How to change the text color in the text field according to the result of <if >

I want to change the text color in the text field to red according to the result, but I don't know how.
In the following cases, I want to change the result of "! Over!" to Red color.
I need your advice. Thank you.

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var GetNextDAY = this.getField("Next-Birth-DAY").value;
var NextDAY = new Date(GetNextDAY);

var TODAY = new Date();
var HowMany = (NextDAY - TODAY)/24/60/60/1000;

if(TODAY > NextDAY){
                                 event.value = ('!Over!');}
                          else{event.value = (HowMany.toFixed()+'Days');};

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