SpannableStringBuilder builder = new SpannableStringBuilder();
String red = "I am RED ";
SpannableString redSpannable= new SpannableString(red);
redSpannable.setSpan(new ForegroundColorSpan(Color.RED), 0, red.length(), 0);
builder.append(redSpannable);
EditText et = (EditText)findViewById(R.id.editText1);
et.setText(builder, BufferType.SPANNABLE);
int position = et.length();
Editable etext = et.getText();
Selection.setSelection(etext, position);