programmatically add body classes with template preprocessing
You can add your class to body element by adding THEMENAME_preprocess_html() to your template.php
Like : 

function MY_THEME_NAME_preprocess_html(&amp;$variables) {
  // Compile a list of classes that are going to be applied to the body element.
  // This allows advanced theming based on context (home page, node of certain type, etc.).
  $variables["classes_array"][] = "blue-bg";
  $variables["attributes_array"]["class"][] = "blue-bg";// For Omega based themes
}


Refer this link for more details.