I wish to alter the colour of a specific section of text within a cell range. I wish to use it as a function which I have named =CTEXT. I wish to make the function visible and working =CTEXT(range, text, colour)

function CTEXT(range, text, color) {
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var cell = sheet.getRange(range);
  var richText = cell.getRichTextValue();
  var newText = richText.getText();
  var startIndex = newText.indexOf(text);
  if (startIndex !== -1) {
    var endIndex = startIndex + text.length;
    var textStyle = SpreadsheetApp.newTextStyle()
      .setForegroundColor(color)
      .build();
    
    var newRichText = richText.copy().setText(newText)
      .setTextStyle(startIndex, endIndex, textStyle)
      .build();
    cell.setRichTextValue(newRichText); 

I have tried this, however, I am quite new to apps script and do not know how this works to its full extent.