Uitextfieldwith dashed line, focus, default dashed color lines in swift

Question

I haven given spaces between chars with NSattributes.kern, need to change focus color of next char border when text enter, should be do with one textfield

class customTextFiled : UITextField {

    for index in 0...charCount {
        let customBorder = CALayer()
        customBorder.frame = CGRect(x: 0, y: frame.height-2, width: 30, height : 10)
        customBorder.borderColor = .green
        layer .insertSublayer(customBorder, at: UInt32(index))
    }
  }

  
  
  textDidChange() {
     // get char count ex 4
      
      layer.sublayers.first[4].backgroundColor = black
      
      layer.sublayers.first[3].backgroundColor = clear
  }
}

when changing the next index layer example 2 layer color black,clearing previous layer example 1 index color, but still 1 index layer showingthin line green(this is default color when created the layer)