div.stub > * { color : red }
div.stub *:not(.foo) { color : lime }

<div class="stub">
<p>This paragraph should be in green characters.</p>
<p class="bar foofoo tut">This paragraph should be in green characters.</p>
<p class="bar foo tut">
     <span class="tut foo2">This paragraph should be in green characters.</span>
</p>
</div>