By using equal values for red, green, and blue, you will get different shades of gray:
<h2 style="background-color:#3c3c3c; color: #FF0000;"> <h2 style="background-color:#616161; color: #FF0000;"> <h2 style="background-color:#787878; color: #FF0000;"> <h2 style="background-color:#b4b4b4;"> <h2 style="background-color:#f0f0f0;"> <h2 style="background-color:#f9f9f9;">