How to get a red asterisk in a <string> entry

You can't do that through xml string resources. This can only be done via code. For this you need to use SpannableStringBuilder and ForegroundColorSpan.

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Here is small example:

TextView text = (TextView)findViewById(R.id.text);

String simple = "Enter your name ";
String colored = "*";
SpannableStringBuilder builder = new SpannableStringBuilder();

builder.append(simple);
int start = builder.length();
builder.append(colored);
int end = builder.length();

builder.setSpan(new ForegroundColorSpan(Color.RED), start, end, 
                Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

text.setText(builder);

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Refer to this for examples on how to style portions of a textview. Here's how you could do it for a red asterisk.

EditText editTxt = new EditText(this);
editTxt.setText("Testing asterisk *");
Spannable str = editTxt.getTxt();
int loc = editTxt.getTxt().toString().indexOf("*");
str.setSpan(new ForegroundColorSpan(Color.RED), loc, 1, Spannable.SPAN_INCLUSIVE_EXCLUSIVE);