TextWatcher textWatcher = new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
    }

    @Override
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        binding.bEnter.setProgress(0);
        if (charSequence.length() > 0){
            int length = 3;
            if (charSequence.length() <= 3) {
                length = charSequence.length();
            }

            Spannable textS = new SpannableString(charSequence.toString());
            textS.setSpan(new ForegroundColorSpan(Color.RED), 0, length, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

            charSequence = textS; // если с текстом всё понятно, то здесь не совсем. Код не работает
        }
    }

    @Override
    public void afterTextChanged(Editable editable) {
    }
};

View.OnFocusChangeListener focus = (view, b) -> {
    if (b) {
        binding.tvPhoneNumber.setHint("+7(***) ***_**_**");
        if (!binding.tvPhoneNumber.getText().toString().startsWith("+7(")) {

            Spannable textS = new SpannableString("+7(");
            textS.setSpan(new ForegroundColorSpan(Color.RED), 0, 2, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
            binding.tvPhoneNumber.setText(textS);// текст появляется, но без изменений со стороны Spannable
            binding.tvPhoneNumber.setSelection(binding.tvPhoneNumber.getText().toString().length());
        }

    } else {
        binding.tvPhoneNumber.setHint(getString(R.string.phone_number));
    }

};