TextView TV = (TextView)findViewById(R.id.mytextview01);

  Spannable WordToSpan = new SpannableString("Your message");        

  WordtoSpan.setSpan(new ForegroundColorSpan(Color.BLUE), 0, WordToSpan.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

  TV.setText(WordToSpan);

  Spannable WordToSpan1 = new SpannableString("Your new message");        

  WordToSpan1.setSpan(new ForegroundColorSpan(Color.RED), 0, WordToSpan1.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

  TV.append(WordToSpan1);