.red { background-color : red }
div.stub > p + p { background-color : lime }

 <div class="stub">
  <p>This paragraph should be unstyled.</p>
  <p class="red">But this one should have a green background.</p>
  <p class="red">And this one should also have a green background.</p>
  <address>This address is only here to fill some space between two paragraphs.</address>
  <p>This paragraph should be unstyled.</p>
 </div>