Try this
For red color,
<string name="hello_worldRed"><![CDATA[<b><font color=#FF0000>Hello world!</font></b>]]></string>
For blue,
<string name="hello_worldBlue"><![CDATA[<b><font color=#0000FF>Hello world!</font></b>]]></string>
In java code,
//red color text
TextView redColorTextView = (TextView)findViewById(R.id.redText);
String redString = getResources().getString(R.string.hello_worldRed)
redColorTextView.setText(Html.fromHtml(redString));
//Blue color text
TextView blueColorTextView = (TextView)findViewById(R.id.blueText);
String blueString = getResources().getString(R.string.hello_worldBlue)
blueColorTextView.setText(Html.fromHtml(blueString));
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